Transmitter and transmission control method

ABSTRACT

In a communication where a retransmission is attained based on a Hybrid-ARQ (Automatic repeat ReQuest) system, retransmission having no gain is reduced, and improvement of the transmission efficiency is intended. A mode determining unit  111  of a base station carries out calculation to obtain a received signal quality difference information indicative of a difference between a received signal quality at the current stage and that of a past stage at a terminal, and supplies to a control unit  112.  The control unit  112  controls a power setting unit  113  based on the received signal quality difference information supplied from the mode determining unit  111,  and thus a transmission power of a signal transmitted from an adaptive coding and modulation unit  13  can be controlled. The present invention can be applied to a base station of a portable telephone communication network, for example.

TECHNICAL FIELD

The present invention relates to a transmission apparatus and a methodfor controlling signal transmission. In more particularly, the presentinvention relates to a transmission apparatus and a method forcontrolling signal transmission for use in a communication system forportable telephones or the like, wherein transmission power, modulationsystems, coding systems and packet synthesizing method are properlyselected in accordance with the received information which are usefulfor adaptive modulation and coding transmission upon signalretransmission, and accordingly, a packet transmission can be achievedin more effective manner. In other words, the present invention relatesto a transmission apparatus and a method for controlling signaltransmission, and in more particularly, the present invention relates toa transmission apparatus and a method for controlling signaltransmission that are able to effectively transmit data from a basestation to a terminal such as a portable telephone or the like.

BACKGROUND ART

An adaptive modulation and coding rate communication system has beenproposed to present a high rate communication while sacrificing noiseresistant characteristic to a user who holds a propagation path of ahigh quality, and to present a low rate communication while keeping thenoise resistant characteristic to a user who only has a propagation pathof a low quality, by changing the coding rate of an error correctioncode and the degree of multilevel modulation in accordance with thequality of the propagation path. Further, as a retransmission system, aHybrid ARQ (Automatic repeat ReQuest) system has been proposed in whichdata retransmission control (ARQ) and error correction code arecombined.

In this case, detail descriptions about the Hybrid ARQ can be found inD. Chase “Code Combining—a Maximum-Likelihood Decoding Approach forCombining an Arbitrary Number of Noisy Packets”, IEEE Trans. Commu.,vol. 33, No. 5, pp. 385-393, May, 1985, and also, can be found in Miki,Arata et. al, “Characteristic of Hybrid ARQ in a situation of W-CDMAdownlink high speed packet transmission” of a technical study report ofthe Society of Electronics, Information and Communication Engineers atVol. 100 No. 343 2000-10.

The communication system employing the adaptive modulation and codingrate (hereinafter selectively referred to as adaptive coding andmodulation system) has been recently introduced into a radiocommunication system. Further, it is expected that the samecommunication system will be introduced, in addition, into acommunication situation using a W-CDMA

(Wideband-Code Division Multiple Access).

In the situation using the adaptive coding and modulation system, thefollowing fundamental procedures are carried out so as to attain theadaptive coding and modulation on the communication between a basestation and a terminal.

1. The terminal determines a received quality of a signal which istransmitted from the base station.

2. The terminal notifies the result of the determination back to thebase station.

3. The base station determines a modulation system and a coding ratewhich provide an optimum performance based on a received signal qualitymessage transmitted from the terminal, and then the base stationtransmits transmission parameters indicative of the determinedmodulation system and the coding rate.

4. The base station transmits user data based on the transmissionparameters.

5. The terminal receives the transmission parameters and carries out adata receiving processing based on the received transmission parameters.

6. If the terminal determines that the data transmitted from the basestation is one concerning a retransmission data, then the terminalcarries out error correction processing after synthesizing the receiveddata containing error in the past with the transmitted data concerningthe retransmission data.

7. If the terminal detects any error in the received data after carryingout the error correction, the terminal transmits a retransmissionrequest, while if the terminal can accurately receive the data, theterminal transmits a new data transmission request to the base station.

8. The above steps 1 to 7 are periodically repeated.

FIG. 1 illustrates a manner of the above mentioned processing sequence.As shown in FIG. 1, illustrated are relations among a downlink controlchannel for notifying the terminal of the transmission parameter fromthe base station, a downlink data channel for transmitting the user datafrom the base station to the terminal, and an uplink control channel fortransmitting a transmission parameter request from the terminal. Anexample shown in this figure is the one in which the above mentionedsteps 1 to 7 are repeated at a predetermined frame period.

That is, as shown in FIG. 1, the terminal determines the received signalquality at the terminal at the current timing point, and then theterminal transmits a received signal quality message indicative of thereceived signal quality to the base station through the uplink controlchannel.

The base station responds to the received signal quality messagetransmitted from the terminal and determines a combination of amodulation system and a coding rate which makes it possible to lower thereceived data error rate at the terminal below a predetermined value.Then, the base station transmits the information indicative of theselected modulation system and the coding rate as a transmissionparameter to the terminal through the downlink control channel.Furthermore, the base station transmits the user data to the terminalthrough the downlink data channel in accordance with the modulationsystem and the coding rate which correspond to the transmissionparameter transmitted to the terminal.

Then the terminal receives the transmission parameter transmitted fromthe base station in the previous stage, and the terminal recognizes themodulation system and the coding rate for the user data transmitted fromthe base station, in accordance with it. Thereafter, the terminalfurther receives the user data transmitted from the base station andcarries out the demodulation based on the demodulation system whichcorresponds to the modulation system designated by the transmissionparameter. Also, the terminal carries out the decoding based on thedecoding system which corresponds to the coding rate designated by thetransmission parameter. The terminal carries out error detection of theuser data which is obtained by the demodulation and the decoding, and,if no error is detected, then the terminal transmits a request messagefor new user data and a received signal quality message to the basestation through the uplink control channel, for example. Meanwhile, therequest message for the new user data contains a message indicating thatthe user data received in the previous stage is able to be normallyreceived.

On the other hand, if any error is detected in the user data obtained bycarrying out the demodulation and the decoding, then the terminaltransmits a retransmission request message requesting that the basestation should retransmit the same user data through the uplink controlchannel to the base station. When the base station receives theretransmission request message, then the base station retransmits theuser data again to the terminal.

The terminal receives the user data which is retransmitted from the basestation, and synthesizes the user data with the error detected user datawhich is received in the previous stage, and the terminal carries outthe error correction processing on the synthesized user data. Thus, theterminal carries out the error detection on the user data after carryingout the error correction processing, and if the terminal detects anyerror in the user data, then the terminal transmits a retransmissionrequest message again to the base station. In this way, the similarprocessing is repeated. On the other hand, if the terminal detects noerror in the user data after carrying out the error correctionprocessing, as described above, the terminal transmits a request messagefor new user data and the received signal quality message to the basestation through the uplink control channel, for example.

FIG. 1 contains terms of downlink data channel, downlink controlchannel, and uplink control channel, and the words “downlink” and“uplink” mean a channel of a signal transmitted from the base station tothe terminal and a channel of a signal transmitted from the terminal tothe base station, respectively. That is, the word “downlink” is utilizedfor a name of a channel through which the signal is transmitted from thebase station to the terminal and the word “uplink” is utilized for aname of a channel through which a signal is transmitted from theterminal to the base station.

The transmission parameter means various parameters which will benecessary when data is transmitted from the base station to theterminal. Therefore, the information designated by the transmissionparameter is not limited to the coding rate, the modulation system atthe base station.

FIG. 2 is a diagram showing an example of an arrangement of aconventional base station which realizes a communication systememploying an adaptive modulation and coding rate (adaptive coding andmodulation system).

The base station is arranged to include a transmission/receptioncompatible unit 1, an inverse spreading unit 2, a power control bitextracting unit 3, a retransmission request message extracting unit 4, areceived signal quality message extracting unit 5, a mode determiningunit 6, a control unit 7, a control data generating unit 8, a coding andmodulation unit 9, a power adjusting unit 10, a spreading unit 11, aretransmission data buffer 12, an adaptive coding and modulation unit13, and an antenna 14.

The base station demodulates a transmission signal from the terminaloperated by a user at the transmission/reception. compatible unit 1 andthe inverse spreading unit 2.

That is, for example, a transmission signal carried out a spectrumspreading is transmitted to the base station from a terminal capable ofdoing radio communication composed of a portable telephone, PDA(Personal Digital Assistant) or the like. The transmitted signal isreceived by the antenna 14 and supplied to the transmission/receptioncompatible unit 1. The transmission/reception compatible unit 1 issupplied with the signal from the antenna 14 and subjects the signal toa necessary processing and then supplies the resultant signal to theinverse spreading unit 2. The inverse spreading unit 2 carries out aninverse spectrum spreading on the signal supplied from thetransmission/reception compatible unit 1 and supplies the resultantsignal to the power control bit extracting unit 3.

The power control bit extracting unit 3 extracts a power control bitfrom the signal supplied from the inverse spreading unit 2. That is, thetransmitted signal transmitted from the terminal to the base stationcontains the power control bit as a one-bit flag indicating a request ofincrease or decrease of power transmitted through the downlink controlchannel as described with reference to FIG. 1. The power control bitextracting unit 3 extracts such a power control bit from the signalsupplied from the inverse spreading unit 2 and transfers the powercontrol bit to the power adjusting unit 10.

The power control bit extracting unit 3 extracts the power control bitfrom the signal supplied from the inverse spreading unit 2 and suppliesthe signal to the retransmission request message extracting unit 4. Theretransmission request message extracting unit 4 extracts aretransmission request message from the signal supplied from the powercontrol bit extracting unit 3.

That is, the transmitted signal transmitted from the terminal to thebase station contains the retransmission request message indicatingwhether a retransmission of the user data is requested or not, asdescribed with reference to FIG. 1. The retransmission request messageextracting unit 4 extracts the retransmission request message from thesignal supplied from the power control bit extracting unit 3 andtransmits the retransmission request message to the control unit 7.

The retransmission request message extracting unit 4 extracts theretransmission request message from the signal supplied from the powercontrol bit extracting unit 3 and also transmits the signal to thereceived signal quality message extracting unit 5. The received signalquality message extracting unit 5 extracts the received signal qualitymessage from the signal supplied from the retransmission request messageextracting unit 4.

That is, the transmitted signal transmitted from the terminal to thebase station contains the received signal quality message indicating thereceived signal quality at the terminal, as described with reference toFIG. 1. The received signal quality message extracting unit 5 extractsthe received signal quality message from the signal supplied from theretransmission request message extracting unit 4 and transmits thereceived signal quality message to the mode determining unit 6.

In this case, the signal exchanged between the terminal and the basestation is composed of frames each having a predetermined time span.Further, each frame is composed of a plural number, e.g., N, of slots ofwhich time span unit is 0.6667 msec (millisecond), for example. Theabove described power control bit is arranged so that the power controlbit is transmitted from the terminal to the base station at each slot.Therefore, the power control bit extracting unit 3 extracts the powercontrol bit at every slot. Further, when the terminal transmits thesignal, the retransmission request message and the received signalquality message are disposed at every frame. Therefore, theretransmission request message extracting unit 4 and the received signalquality message extracting unit 5 carry out respective extractingoperations at every frame to extract the retransmission request messageand the received signal quality message.

The mode determining unit.6 determines an optimum modulation system andcoding rate in accordance with the received signal quality message andthe state of the resources owned by the base station, and assigns coderesources and power resources to the user (terminal).

Accordingly, now a term of transmission mode is taken as a combinationof the modulation system and the coding rate, then the mode determiningunit 6 determines the transmission mode in accordance with the receivedsignal quality message supplied from the received signal quality messageextracting unit 5 and the resources of the base station. Then, the modedetermining unit 6 supplies the information of the transmission mode tothe control unit 7.

In this case, there are various kinds of possible combinations of thecoding rates and the modulation systems and hence the transmission modecan take various types of modes, but in here, in order to simplify thedescription thereof, description will be made on three kinds oftransmission modes, i.e., modes of #0 to #2 as shown in FIG. 3.

As shown in FIG. 3, R=½ and R=¾ are prepared for examples of the codingrates (coding systems). The coding rate of R=½ means that a redundantbit of one bit is added to every one bit of input data. The coding rateof R=¾ means that a redundant bit of one bit is added to every threebits of input data. If the data is coded at the coding rate of R=½, ascompared with a case in which the data is coded at the coding rate ofR=¾, the whole data contains a larger number of redundant bits relativeto the input data. Therefore, the error correction capability isstrengthen but only small amount of data can be transmitted. Conversely,if the data is coded at the coding rate of R=¾, as compared with a casein which the data is coded at the coding rate of R=½, the whole datacontains a smaller number of redundant bits relative to the input data.Therefore, the error correction capability is inferior to the case inwhich the data is coded at the coding rate of R=½ but a large amount ofdata can be transmitted.

As shown in FIG. 3, an QPSK (Quadrature Phase Shift Keying) and a 16QAM(Quadrature Amplitude Modulation) are prepared for examples ofmodulation systems. As shown in FIG. 4, if the QPSK modulation system isselected, the coded data are converted into symbols composed of twobits, and these symbols are mapped on any of four-symbol group (see FIG.4A). Conversely, if the 16QAM modulation system is selected, the codeddata are converted into symbols composed of four bits, and these symbolsare mapped on any of 16-symbol group (see FIG. 4B). If it is assumedthat a symbol rate capable of being transmitted is constant, themodulation system of the 16QAM has a larger amount of data actuallybeing transmitted than the modulation system of the QPSK. However, sincethe modulation system of the 16QAM has a smaller intersymbol distancethan the modulation system of the QPSK, the noise characteristic is tobe deteriorated.

As shown in FIG. 3, a combination of the coding rate of R=½ and themodulation system of the QPSK, a combination of the coding rate of R=½and the modulation system of the 16QAM, and a combination of the codingrate of R=¾ and the modulation system of the 16QAM are defined astransmission modes of #0, #1, and #2, respectively. Therefore, therelation of the data transfer rate among these transmission modes is tobe given as follows. That is, the transmission mode of #0 (R=½,QPSK)<the transmission mode of #1 (R=½, 16QAM)<the transmission mode of#2 (R=¾, 16QAM). On the other hand, the relation of the noise withstandcharacteristic among these transmission modes can be given as follows.That is, the transmission mode of #0 (R=½, QPSK)> the transmission modeof #1 (R=½, 16QAM)> the transmission mode of #2 (R=¾, 16QAM).

According to the adaptive coding and modulation system, the coding rateand the modulation system can be selectively determined depending on thenature of the signal transmission path. That is, if the noise level islow and the transmission path is good (i.e., the received signal qualityat the terminal is good), a combination of the coding rate and themodulation system providing a large amount of data transfer rate(transmission mode) is selected to carry out effective datatransmission. Conversely, if the noise level is high and thetransmission path is bad (i.e., the received signal quality at theterminal is bad), a combination of the coding rate and the modulationsystem providing a high noise withstand characteristic (transmissionmode) is selected to carry out data transmission in which the datatransfer rate is suppressed and error correction characteristic isstrengthened.

Now description is again made on a matter concerning FIG. 2. Initially,the control unit 7 confirms the retransmission request messagetransmitted from the retransmission request message extracting unit 4.If it is confirmed that there is a retransmission request message, thecontrol unit 7 transmits information indicative of a transmission modeidentical to that upon initially transmitting the user data (i.e., thetransmission mode upon transmitting the first user data) and aretransmission flag indicating that this transmission is aretransmission, to the control data generating unit 8 and the adaptivecoding and modulation unit 13. Further, if there is no retransmissionrequest, the control unit 7 transfers a transmission mode determined bythe mode determining unit 6 to the control data generating unit 8 andthe adaptive coding and modulation unit 13.

The control data generating unit 8 makes the information indicative ofthe transmission mode supplied from the control unit 7 be involved inthe transmission parameter to be transmitted through the downlinkcontrol channel which is described with reference to FIG. 1. Further,the control data generating unit 8 generates control data having thetransmission parameter involved therein and supplies the control data tothe coding and modulation unit 9. If the control data generating unit 8is supplied with a retransmission request flag in addition to theinformation indicative of the transmission mode from the control unit 7,the control data generating unit 8 makes the retransmission request flagbe involved in the transmission parameter. The coding and modulationunit 9 subjects the control data supplied from the control datagenerating unit 8 to a coding and modulation processing which iseffected in a previously determined system. Then, the coding andmodulation unit 9 supplies the resultant modulated signal to the poweradjusting unit 10.

The power adjusting unit 10 determines a level of transmission power fortransmitting data through the downlink control channel described withreference to FIG. 1, in accordance with the power control bit suppliedfrom the power control bit extracting unit 3. That is, as describedabove, the power control bit is a one-bit flag, for example, and whenthe power control bit is 1, then the power adjusting unit 10 increasesthe transmission power for the downlink control channel by 1 dB, andwhen the power control bit is 0, then the power adjusting unit 10decreases the transmission power for the downlink control channel by 1dB. Thus, the modulated signal supplied from the coding and modulationunit 9 is processed. In this way, it becomes possible to provide anarrangement for transmitting data through the downlink control channelto the terminal at an optimum power. In a communication using the CDMA,this manner of controlling the transmission power in the downlinkcontrol channel has been generally employed.

The modulated signal carried out the transmission power adjustment inthe power adjusting unit 10 is supplied to the spreading unit 11.

Meanwhile, the adaptive coding and modulation unit 13 is supplied withthe packet data having the user data disposed therein, and to betransmitted through the downlink data channel that is described withreference to FIG. 1. The adaptive coding and modulation unit 13 subjectsthe packet data to a coding processing by using the coding rate which isindicated in the transmission mode information supplied from the controlunit 7. Further, the adaptive coding and modulation unit 13 effects themodulation processing on the coded packed data by using the modulationsystem which is indicated in the transmission mode information. Thus,the modulated signal obtained by the coding and modulating the packetdata is supplied to the spreading unit 11.

The packet data supplied to the adaptive coding and modulation unit 13is also supplied to the retransmission data buffer 12. Theretransmission data buffer 12 temporarily stores therein the packetdata. When the retransmission request message supplied from theretransmission request message extracting unit 4 indicates a request ofretransmission, the control unit 7 controls the retransmission databuffer 12 so that the packet data to be subjected to the retransmissionis supplied to the adaptive coding and modulation unit 13. In this case,the adaptive coding and modulation unit 13 effects the coding processingand modulation processing as described above on the packet data suppliedfrom the retransmission data buffer 12, i.e., the packet data identicalto that transmitted in the previous step. Then, the resultant modulatedsignal is supplied to the spreading unit 11. In this way, the packetdata is again transmitted.

FIG. 5 is a diagram showing an arrangement of the adaptive coding andmodulation unit 13 in which three transmission modes, i.e., modes of #0to #2 shown in FIG. 3 are prepared.

The packet data inputted into the adaptive coding and modulation unit 13is supplied to a switch 21.

If the transmission mode information supplied from the control unit 7indicates the transmission mode #0, the switch 21 selects a terminal 21a and a switch 24 selects a terminal 24a.

The terminal 21 a is connected to a coding unit 22 a. Therefore, if thetransmission mode is #0, the packet data is supplied from the switch 21to the coding unit 22 a. The coding unit 22 a encodes the packet datasupplied thereto at the coding rate of R=½ so that an error correctioncode is added to the data. The resultant coded data is supplied to aQPSK modulating unit 23 a. The QPSK modulating unit 23 a effects a QPSKmodulation on the coded data supplied from the coding unit 22 a so thatmodulated symbols are mapped to form a constellation. The resultantmodulated signal is supplied to the terminal 24 a of the switch 24. Whenthe transmission mode is #0, as described above, the switch 24 selectsthe terminal 24 a. Therefore, the modulated signal outputted from theQPSK modulating unit 23 a is supplied through the switch 24 to thespreading unit 11 (FIG. 2).

In this case, if the transmission mode information supplied from thecontrol unit 7 indicates the transmission mode #1, the switch 21 selectsa terminal 21 b and the switch 24 selects a terminal 24 b. The terminal21 b is connected to a coding unit 22 b. Therefore, if the transmissionmode is #1, the packet data is supplied from the switch 21 to the codingunit 22 b. The coding unit 22 b encodes the packet data supplied theretoat the coding rate of R=½ and the resultant coded data is supplied to a16QAM modulating unit 23 b. The 16QAM modulating unit 23 b effects a16QAM modulation on the coded data supplied from the coding unit 22 band the resultant modulated signal is supplied to the terminal 24 b ofthe switch 24. When the transmission mode is #1, as described above, theswitch 24 selects the terminal 24 b. Therefore, the modulated signaloutputted from the 16QAM modulating unit 23 b is supplied through theswitch 24 to the spreading unit 11 (FIG. 2).

Further, if the transmission mode information supplied from the controlunit 7 indicates the transmission mode #2, the switch 21 selects aterminal 21 c and the switch 24 selects a terminal 24 c. The terminal 21c is connected to a coding unit 22 c. Therefore, if the transmissionmode is #2, the packet data is supplied from the switch 21 to the codingunit 22 c. The coding unit 22 c encodes the packet data supplied theretoat the coding rate of R=¾ and the resultant coded data is supplied to a16QAM modulating unit 23 c. The 16QAM modulating unit 23 c effects a16QAM modulation on the coded data supplied from the coding unit 22 cand the resultant modulated signal is supplied to the terminal 24 c ofthe switch 24. When the transmission mode is of #2, as described above,the switch 24 selects the terminal 24 c. Therefore, the modulated signaloutputted from the 16QAM modulating unit 23 c is supplied through theswitch 24 to the spreading unit 11 (FIG. 2).

Now description will be again provided with reference to FIG. 2. Thespreading unit 11 effects the spectrum spreading on the modulated signalsupplied from the power adjusting unit 10 and the modulated signalsupplied from the adaptive coding and modulation unit 13 by usingdifferent spreading codes. A spread signal obtained by these operationsis supplied to the transmission/reception compatible unit 1. Thetransmission/reception compatible unit 1 effects a necessary processingon the spread signal supplied from the spreading unit 11 and transmitsto the terminal as a radio wave from the antenna 14.

In this case, the modulated signal supplied from the power adjustingunit 10 is to be a signal transmitted through the downlink controlchannel shown in FIG. 1 and the modulated signal supplied from theadaptive coding and modulation unit 13 is to be a signal transmittedthrough the downlink data channel shown in FIG. 1.

FIG. 6 is a diagram showing an example of an arrangement of aconventional terminal which can realize a communication system employingan adaptive modulation and coding rate (adaptive coding and modulationsystem).

The terminal (user terminal) is arranged to include atransmission/reception compatible unit 31, an inverse spreading unit 32,a control channel received signal quality estimating unit 33, a powercontrol bit generating unit 34, a data channel received signal qualityestimating unit 35, a received signal quality message generating unit36, a control data demodulating and decoding unit 37, a control unit 38,a user data demodulating and decoding unit 39, an error detecting unit40, are transmission request message generating unit 41, aretransmission request message inserting unit 42, a received signalquality message inserting unit 43, a power control bit inserting unit44, a spreading unit 45, a received signal buffer 46, and an antenna 47.

The transmitted signal transmitted from the base station is received bythe antenna 47. The received signal is subjected to the necessaryprocessing in the transmission/reception compatible unit 31, andthereafter supplied to the inverse spreading unit 32. The inversespreading unit 32 effects an inverse spectrum spreading on the signalsupplied from the transmission/reception compatible unit 31 so that thesignal is divided into a signal for the downlink data channel and asignal for the downlink control channel which are described withreference to FIG. 1. The inverse spreading unit 32 supplies the signalfor the downlink control channel to the control channel received signalquality estimating unit 33 and the control data demodulating anddecoding unit 37. Further, the inverse spreading unit 32 supplies thesignal for the downlink data channel to the data channel received signalquality estimating unit 35 and the user data demodulating and decodingunit 39.

The control channel received signal quality estimating unit 33 estimatesa signal to noise ratio (SNR (Signal to Noise Ratio)) based on a pilotsignal which derives from time division multiplexing effected in thedownlink control channel. That is, although description is not providedwith reference to FIG. 2, in the base station, the spreading unit 11carries out a time division multiplexing on a predetermined pilot signalwith the demodulated signal supplied from the power adjusting unit 10.Thereafter, the spreading unit 11 carries out the spectrum spreading onthe signal. Therefore, the signal transmitted through the downlinkcontrol channel contains the pilot signal in addition to the modulatedsignal supplied from the power adjusting unit 10. The control channelreceived signal quality estimating unit 33 estimates the SNR of thesignal supplied from the inverse spreading unit 32 through the downlinkcontrol channel by using the pilot signal contained in the signal. Then,the control channel received signal quality estimating unit supplies theestimated SNR to the power control bit generating unit 34.

The power control bit generating unit 34 responds to the estimated SNRof the downlink control channel in such a manner that if the estimatedSNR is better than a desired SNR then a power control bit of a value “0”is outputted to the power control bit inserting unit 44 while if thesame is worse than the desired value then a power control bit of a value“1” is outputted to the power control bit inserting unit 44. In thiscase, the SNR estimation in the control channel received signalestimating unit 33 and the power control bit generation in the powercontrol bit generating unit 34 are executed for every slot. Then, asdescribed above, the base station described with reference to FIG. 2controls the transmission power of the downlink control channel based onthe power control bit so that the terminal can always receive the signalof the downlink control channel at a constant SNR.

The control data demodulating and decoding unit 37 demodulates anddecodes the signal supplied from the inverse spreading unit 32 throughthe downlink control channel, separates the control data from thesignal, and supplies the same to the control unit 38.

The control unit 38 detects the information concerning the coding rateand the modulation system to be applied to the downlink data channel,i.e., the transmission mode information, which is disposed in thecontrol data supplied from the control data demodulating and decodingunit 37. Then, the control unit carries out mode setting (control) forthe user data demodulating and decoding unit 39.

That is, as shown in a flowchart of FIG. 7, initially at step S1, thecontrol unit 38 detects the transmission mode from the control datasupplied from the control data demodulating and decoding unit 37 and theprocessing proceeds to step S2. At step S2, the control unit 38 examineswhether the modulation system indicated by the transmission mode is theQPSK modulation or not. At step S2, if it is determined that themodulation system indicated by the transmission mode is the QPSKmodulation, the processing proceeds to step S3. In this step S3, thecontrol unit 38 demodulates the signal of the downlink data channelbased on the QPSK manner, and controls the user data demodulating anddecoding unit 39 so that this unit decodes the signal at the coding rateof R=½. Thereafter, the control unit 38 awaits the next control data tobe supplied from the control data demodulating and decoding unit 37. Theprocessing returns from step S3 to S1, and the same processing sequenceis repeated in a similar manner.

At step S2, if it is determined that the modulation system indicated bythe transmission mode is not the QPSK modulation, the processingproceeds to step S4. In this step S4, the control unit 38 examineswhether the modulation system indicated by the transmission mode is the16QAM and the coding rate indicated by the transmission mode is R=½ ornot. At step S4, if it is determined that the modulation systemindicated by the transmission mode is the 16QAM and the coding rateindicated by the transmission mode is R=½, then the processing proceedsto step S5. In this step S5, the control unit 38 demodulates the signalof the downlink data channel based on the 16QAM manner, and controls theuser data demodulating and decoding unit 39 so that this unit decodesthe signal at the coding rate of R=½. Thereafter, the control unit 38awaits the next control data to be supplied from the control datademodulating and decoding unit 37. The processing returns from step S5to S1, and the same processing sequence is repeated in a similar manner.

At step S4, if it is determined that the transmission mode informationdoes not designate the combination of the modulation system of the 16QAMand the coding rate of R=½, the processing proceeds to step S6. In thisstep S6, the control unit 38 examines whether the modulation systemindicated by the transmission mode is the 16QAM or not and whether thecoding rate indicated by the transmission mode is R=¾ or not. At stepS6, if it is determined that the modulation system indicated by thetransmission mode is the 16QAM and the coding rate indicated by thetransmission mode is R=¾, then the processing proceeds to step S7. Inthis step, the control unit 38 demodulates the signal of the downlinkdata channel based on the 16QAM manner, and controls the user datademodulating and decoding unit 39 so that this unit decodes the signalat the coding rate of R=¾. Thereafter, the control unit 38 awaits thenext control data to be supplied from the control data demodulating anddecoding unit 37. The processing returns from step S7 to S1, and thesame processing sequence is repeated in a similar manner.

At step S6, if it is determined that the transmission mode informationdoes not designate the combination of the modulation system of the 16QAMand the coding rate of R=¾, this determination means that thetransmission mode information does not designate any of the threecombinations of the modulation system and the coding rate as shown inFIG. 3. In this event, the control unit 38 determines that thetransmission mode is erroneous one, and hence the control unit 38 takesno particular action in controlling the user data demodulating anddecoding unit 39. Thus, the control unit 38 awaits the next control datato be supplied from the control data demodulating and decoding unit 37,and the processing returns from step S6 to S1, and the same processingsequence is repeated in a similar manner.

Now description will be again made with reference to FIG. 6. The datachannel received signal quality estimating unit 35 estimates the SNR ofthe signal of the downlink data channel supplied from the inversespreading unit 32. When the data channel received signal qualityestimating unit 35 estimates the SNR, the data channel received signalquality estimating unit 35 utilizes a pilot symbol subjected to the timedivision multiplexing on the downlink data channel or a pilot channelsymbol transmitted together with the downlink data channel in a parallelmanner.

Although description is not provided yet with reference to FIG. 2, thespreading unit 11 effects the time division multiplexing on thepredetermined pilot signal with the demodulated signal supplied from theadaptive coding and modulation unit 13. Thereafter, the spreading unit11 carries out the spectrum spreading. Therefore, the signal of thedownlink data channel contains the pilot signal. Further, the spreadingunit 11 effects the spectrum spreading on another pilot signal with aspreading code different from a spreading code which is utilized for theeffecting spectrum spreading on the demodulated signal supplied from thepower adjusting unit 10 or the adaptive coding and modulation unit 13.Then, the pilot signal is supplied through the transmission/receptioncompatible unit 1 to the antenna 14 from which the pilot signal istransmitted through the downlink data channel and the downlink controlchannel in parallel.

The data channel received signal quality estimating unit 35 estimatesthe SNR of the signal of the downlink data channel supplied from theinverse spreading unit 32 by using the pilot signal contained in thesignal or the pilot signal transmitted in parallel together with thesignal of the downlink data channel. Then, the estimated SNR is suppliedto the received signal quality message generating unit 36.

The received signal quality message generating unit 36 handles theestimated SNR of the downlink data channel supplied from the datachannel received signal quality estimating unit 35 as the receivedsignal quality at the terminal, and generates a received signal qualitymessage of a predetermined message format so that the message indicatesthe received signal quality. Then, the received signal quality messagegenerating unit 35 supplies the received signal quality message to thereceived signal quality message inserting unit 43.

In this case, the data channel received signal quality estimating unit35 estimates the SNR of the downlink data channel for each frame and thereceived signal quality message generating unit 36 generates thereceived signal quality message also for each frame.

On the other hand, the user data demodulating and decoding unit 39carries out decoding and demodulation on the signal of the downlink datachannel supplied from the inverse spreading unit 32 under the control ofthe control unit 38 which is described with reference to FIG. 7. Theresultant user data obtained by the operation is supplied to the errordetecting unit 40. When the user data demodulating and decoding unit 39decodes the signal of the downlink data channel, the user datademodulating and decoding unit 39 carries out user data error correctionby using the error correction code contained in the signal as aredundancy bit.

The error detecting unit 40 carries out a parity detection by usingCyclic Redundancy Check (CRC), for example. That is, the error detectingunit 40 examines whether the user data decoded by the user datademodulating and decoding unit 39 contains any error or not, and theerror detecting unit 40 supplies the result of the examination to theretransmission request message generating unit 41 and the receivedsignal buffer 46.

If the retransmission request message generating unit 41 receives anexamination result indicating that there is no error contained thereinfrom the error detecting unit 40, then the retransmission requestmessage generating unit 41 generates a message having a value of “0”,for example, and supplies the message to the retransmission requestmessage inserting unit 42. Conversely, if the retransmission requestmessage generating unit 41 receives an examination result indicatingthat there is some error contained therein from the error detecting unit40, then the retransmission request message generating unit 41 generatesa message having a value of “1”, for example, and supplies the messageto the retransmission request message inserting unit 42.

The retransmission request message inserting unit 42 carries out framingon the retransmission request message supplied from the retransmissionrequest message generating unit 41 with the signal of the uplink controlchannel described with reference to FIG. 1, and supplies the resultantsignal to the received signal quality message inserting unit 43. Thereceived signal quality message inserting unit 43 carries out framing onthe received signal quality message supplied from the received signalquality message generating unit 36 with the signal of the uplink controlchannel supplied from the retransmission request message inserting unit42. The resultant signal is supplied to the power control bit insertingunit 44. The power control bit inserting unit 44 carries out framing onthe power control bit supplied from the power control bit generatingunit 34 with the signal of the uplink control channel supplied from thereceived signal quality message inserting unit 43. The resultant signalis supplied to the spreading unit 45. The spreading unit 45 effects thespectrum spreading on the signal of the uplink control channeltransmitted from the power control bit inserting unit 44, and suppliesthe resultant signal obtained by the operation to thetransmission/reception compatible unit 31.

The transmission/reception compatible unit 31 effects a necessaryprocessing on the spread signal transmitted from the spreading unit 45and transmits the signal through the antenna 47.

On the other hand, as described above, the user data demodulating anddecoding unit 39 demodulates the signal of the downlink data channel anddecodes coded data obtained as a result of the demodulation. However,the user data demodulating and decoding unit 39 carries out anotheroperation than the decoding of the coded data as described above. Thatis, user data demodulating and decoding unit 39 supplies the coded datato the received signal buffer 46.

The received signal buffer 46 temporarily stores therein the coded datasupplied from the user data decoding unit 39 and supplies the storedcoded data to the user data demodulating and decoding unit 39 undercontrol of the control unit 38.

That is, if any error is detected in the user data disposed in thedownlink data channel, the retransmission request message generatingunit 41 generates a retransmission request message requesting a signalretransmission, as described above. This retransmission request messageis disposed in the uplink control channel and transmitted.

When the base station having the arrangement illustrated in FIG. 2receives the retransmission request message requesting the signalretransmission, as described above, the base station again transmits theuser data (i.e., packet data having the user data disposed therein)identical to that transmitted upon the previous transmission step.

When the base station again transmits the user data, the signal of thedownlink data channel containing the user data carried out theretransmission process is transmitted to the antenna 47, thetransmission/reception compatible unit 31 and the inverse spreading unit32 in which processing similar to those described above are carried out.Thereafter, the resulting signal is supplied to the user datademodulating and decoding unit 39.

Further, when the base station retries to transmit the user data, asdescribed with reference to FIG. 2, the control data is made to containa retransmission flag indicating that the transmission is aretransmitted one. When the control unit 38 recognizes that the controldata contains the retransmission flag, the control unit 38 controls thereceived signal buffer 46 so that the received signal buffer suppliesthe coded data corresponding to the user data concerning theretransmission stored in the received signal buffer 46 to the user datademodulating and decoding unit 39.

Accordingly, when the user data is again transmitted to the terminal,the user data demodulating and decoding unit 39 is supplied with thesignal of the downlink data channel having the user data concerning theretransmission disposed therein from the inverse spreading unit 32. Inaddition, the user data demodulating and decoding unit 39 is suppliedwith the coded data corresponding to the user data concerning theretransmission from the received signal buffer 46.

If the control data contains the retransmission flag, the control unit38 controls the received signal buffer 46 in a manner as describedabove. Also the control unit 38 controls the user data demodulating anddecoding unit 39 so that the user data demodulating and decoding unit 39synthesizes the coded data.

In this case, the user data demodulating and decoding unit 39demodulates the signal of the downlink data channel having the user dataconcerning the retransmission disposed therein to obtain the coded data.Thereafter, the user data demodulating and decoding unit 39 synthesizesthe coded data of the retransmission with the coded data supplied fromthe received signal buffer 46 so as to obtain coded data in which largerenergy is allocated to each one-bit amount of the user data. The codeddata is supplied from the user data demodulating and decoding unit 39 tothe received signal buffer 46 and stored in the received signal buffer46 in a manner of overwriting, for example. Further, the user datademodulating and decoding unit 39 decodes the coded data having thelarger energy allocated to each one-bit amount of the user data torestore the user data, and supplies the same to the error detecting unit40.

As described above, the error detecting unit 40 examines whether theuser data supplied from the user data demodulating and decoding unit 39contains any error or not. If it is determined that there is no errorcontained therein, the detecting unit 40 outputs the result of theexamination. The result of determination indicating no error is alsosupplied to the received signal buffer 46 in addition to theretransmission request message generating unit 41.

When the received signal buffer 46 receives the result of theexamination indicating that there is no error contained in the userdata, the received signal buffer 46 clears the coded data stored thereincorresponding to the user data which is confirmed that there is no errorcontained therein.

As described above, if it is determined that the user data contains anyerror, the terminal requests the base station to send the signal again,synthesizes the data concerning the retransmission and the data receivedin the previous step together, and allocates larger energy to eachone-bit amount of the user data by using the synthesized gain derivingfrom the synthesizing operation, whereby the error contained in the userdata is restored. This series of signal retransmission scheme is theHybrid-ARQ.

According to the adaptive coding and modulation system, the datatransmission speed can be varied in accordance with the received signalcondition (received signal quality) at the terminal. Therefore, the datais able to be transmitted to the terminal side efficiently.

Meanwhile, in the above arrangement, the base station determines whetherit is necessary to retry signal transmission depending on theretransmission request message transmitted from the terminal. The dataof the retransmission is synthesized with the data transmitted in theprevious step. Therefore, if coincidence or any improvement is foundbetween the initial data transmission and the current data transmissionin the received signal quality, then it is expected that the signal tointerference ratio is improved and the transmission efficiency can bealso improved. In the actual practice, however, there can be broughtabout a situation in which the propagation path is deteriorated at thedata retransmission time as compared with at the initial datatransmission time. In such a situation, there can be taken place inwhich synthesizing the data of retransmission with data of a previousstep does not bring an improvement in the transmission efficiency (i.e.,no gain can be obtained by synthesizing the data of the retransmission).

Furthermore, there can be brought about a situation in which, contraryto the above case, improvement is found in the propagation pathcharacteristic upon retransmitting the data as compared with upon theinitial data transmission. This fact follows that the data ofretransmission is transmitted by using an excessive energy, andresultantly the radio communication resources are to be consumeduselessly.

DISCLOSURE OF THE INVENTION

The present invention is made in view of the above aspect. Therefore, itis an object of the present invention to propose a solution in which atransmission parameter is controlled depending on the received signalquality at the terminal, so that a retransmission achieving no gain isreduced and useless radio communication resources are suppressed,whereby transmission efficiency can be improved.

According to the present invention, there is provided a transmissionapparatus characterized by including differential informationcalculating means for carrying out calculation to obtain differentialinformation regarding the difference in the received signal qualities atthe terminal and control means for controlling a transmission parameterupon transmitting the data to the terminal based on the differentialinformation.

According to the present invention, there is provided a method forcontrolling signal transmission characterized by including steps ofcalculating differential information to obtain differential informationregarding the difference in the received signal qualities at theterminal, and controlling a transmission parameter upon transmitting thedata to the terminal based on the differential information.

According to the present invention, there is provided a programcharacterized by including comprising steps of calculating differentialinformation to obtain differential information regarding the differencein the received signal qualities at the terminal, and controlling atransmission parameter upon transmitting the data to the terminal basedon the differential information.

According to the transmission apparatus, the method for controllingsignal transmission, and the program of the present invention, thedifferential information concerning the difference between the receivedsignal qualities at the terminal, and the transmission parameter upontransmitting data to the terminal is controlled based on the differenceinformation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a conventional manner of datatransmission;

FIG. 2 is a block diagram showing one example of an arrangement of aconventional base station;

FIG. 3 is a diagram showing examples of transmission modes;

FIG. 4A is a diagram illustrating the mapping of the data in accordancewith a QPSK modulation system;

FIG. 4B is a diagram illustrating the mapping of the data in accordancewith a 16QAM modulation system;

FIG. 5 is a block diagram showing an example of an arrangement of anadaptive coding and modulation unit 13;

FIG. 6 is a block diagram showing one example of an arrangement of aconventional terminal;

FIG. 7 is a flowchart for explaining a data receiving processing at theterminal;

FIG. 8 is a block diagram showing an example of an arrangement of oneembodiment of a base station to which the present invention is applied;

FIG. 9 is a diagram showing a specific example of a relation between thedata retransmission processing and the received signal quality;

FIG. 10 is a flowchart for explaining a processing at the base station;

FIG. 11 is a flowchart showing a first embodiment of a retransmissionprocessing;

FIG. 12 is a flowchart showing a second embodiment of a retransmissionprocessing;

FIG. 13 is a flowchart showing a third embodiment of a retransmissionprocessing;

FIG. 14 is a flowchart showing a fourth embodiment of a retransmissionprocessing;

FIG. 15 is a flowchart showing a fifth embodiment of a retransmissionprocessing; and

FIG. 16 is a block diagram showing an example of an arrangement of oneembodiment as a computer to which the present invention is applied.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 8 is a diagram showing an example of an arrangement of oneembodiment of a base station (apparatus) to which the present inventionis applied. In this figure, like parts corresponding to those parts inFIG. 2 are identified by the same reference numerals. Therefore, theywill not be described in the following description.

As shown in FIG. 8, the base station is arranged to include atransmission/reception compatible unit 1, an inverse spreading unit 2, apower control bit extracting unit 3, a retransmission request messageextracting unit 4, a mode request message extracting unit 5, a modedetermining unit 111, a control unit 112, a control data generating unit8, a coding and modulation unit 9, a power adjusting unit 10, aspreading unit 11, a data buffer 12, an adaptive coding and modulationunit 13, a power setting unit 113, and a data SNR buffer 114.

Accordingly, the base station shown in FIG. 8 has the mode determiningunit 111 and the control unit 112 provided in lieu of the modedetermining unit 6 and the control unit 7. Further, the base station isadditionally provided with the power setting unit 113 and the data SNRbuffer 114. Remaining components constituting the base station arearranged in a fundamentally similar manner as those of the base stationshown in FIG. 2.

The mode determining unit 111 determines the transmission mode based onthe received signal quality message supplied from the received signalquality message extracting unit 5 and the resources of the base stationin a manner similar to that of the mode determining unit 6 shown in FIG.2. Further, the mode determining unit 111 is supplied with theretransmission request message from the retransmission request messageextracting unit 4. If the mode determining unit 111 receives aretransmission request message requesting a retransmission, the modedetermining unit carries out arithmetic operation to determine thedifference between the received signal quality at the current step(current received signal quality) indicated by the received signalquality supplied from the received signal quality message extractingunit 5 and the received signal quality of a previous step stored in thedata SNR buffer 114. Then, the mode determining unit supplies thedifference between the received signal qualities (hereinafter sometimesreferred to as received signal quality difference) to the control unit112. Further, the mode determining unit 111 determines the transmissionmode based on the received signal quality difference depending onnecessity. Furthermore, the mode determining unit 111 supplies thereceived signal quality at the current step indicated by the receivedsignal quality message supplied from the received signal quality messageextracting unit 5 to the control unit 112.

Similarly to the control unit 6 shown in FIG. 2, the control unit 112controls the retransmission data buffer 12 in accordance with theretransmission request message supplied from the retransmission requestmessage extracting unit 4. Also, the control unit 112 controls thetransmission parameter of the adaptive coding and modulation unit 13,i.e., the coding rate and the modulation system, in accordance with thetransmission mode information supplied from the mode determining unit111. Further, similarly to the control unit 6 shown in FIG. 2, thecontrol unit 112 supplies information necessary for generating controldata to the control data generating unit 8. Further, the control unit112 controls the transmission parameter of the power setting unit 113,i.e., the transmission power of a signal outputted from the adaptivecoding and modulation unit 13, based on the difference informationsupplied from the mode determining unit 111. The control unit 112supplies the received signal quality of the current step supplied fromthe mode determining unit 111 to the data SNR buffer 114 depending onthe necessity. Furthermore, the control unit 112 updates the receivedsignal quality information stored in the data SNR buffer 114 dependingon necessity.

The power setting unit 113 adjusts the transmission power of the signaloutputted from the adaptive coding and modulation unit 13 in accordancewith the control of the control unit 112 and supplies the same to thespreading unit 11.

The data SNR buffer 114 stores therein the information of the receivedsignal quality supplied from the control unit 112 or other informationlike that.

The base station shown in FIG. 8 carries out control operations whichare different from the conventional manner of control. The differentpoints are itemized as follows.

1. When new data is to be transmitted, the control unit 112 reserves areceived signal quality message received in a time slot of thetransmitted data in the data SNR buffer 114.

2. If the retransmission request message extracted by the retransmissionrequest message extracting unit 4 indicates a request of retransmission,then the mode determining unit 111 executes the following operations.

(1) To acquire the received signal quality Qprv by transferring the samefrom the data SNR buffer 114.

(2) To compare the received signal quality Qprv of the previous stepwith the received signal quality Qnow of the current report.

(3) If it is determined that the received signal quality Qnow isdegraded by a predetermined threshold value THx[dB] (DeciBel) withrespect to the received signal quality Qprv of the previous step, themode determining unit determines that it is necessary to change thetransmission parameter. Thus, the following processing of No. 3 or 4 iscarried out. If the determination takes any mode other than the aboveone, the mode determining unit determines that it is unnecessary tochange the transmission parameter. Thus, the following processing of No.5 is carried out.

3. If there is an allowance to increase the transmission power by y dB,the data retransmission is tried in the following manner. In this case,y is given by an expression (past received signal quality Qprv−currentreceived signal quality Qnow−THx).

(1) The transmission power is increased by Pup amount where the value ofPup is one satisfying equations of ydB≦Pup≦Pavl. In this case, the valueof Pup is the maximum amount of resources allowable to be assigned to asingle user at this timing point.

(2) In this case, the mode determining unit selects a modulation systemand a coding rate which are identical to those used in the previousstep, respectively.

(3) To update the value of the received signal quality Qprv stored inthe data SNR buffer 114. The updated received signal quality Qprvderives from an operation of Qprv←Qprv+Qnow+Pup. Therefore, if Pup=y,the past received signal quality is updated by being replaced with2Qprv−THx.

(4) Transmission is made through the downlink control channel to theterminal so as to inform the terminal that the transmission data is aretransmission data, the modulation system and the coding system (codingrate) are same as those employed when the user data was transmitted inthe previous step. In this case, the terminal is allowed to synthesizethe data temporarily stored in the received signal buffer 46 (FIG. 6)with the retransmission data. Since the terminal has the samearrangement as that described with reference to FIG. 6, the descriptionthereof will not be made.

(5) The user data is again transmitted.

4. If there is no allowance to increase the transmission power by y dB,the data retransmission is tried in the following manner. In this case,similarly to the above-described case, y is given by an expression (pastreceived signal quality Qprv−current received signal quality Qnow−THx).

(1) The modulation system and the coding system is selected depending onthe current received signal quality Qnow.

(2) The value Qprv stored in the data SNR buffer 114 is updated bychanging into the current received signal quality Qnow.

(3) Transmission is made through the downlink control channel so as toinform that the transmission data is a retransmission data, themodulation system and the coding system (coding rate) are different fromthose employed when the user data is transmitted in the previous step.In this case, the terminal does not synthesize the data stored in thereceived signal buffer 46 with the transmitted data.

(4) The user data is again transmitted.

5. The data retransmission is tried in the following manner.

(1) The mode determining unit selects a transmission power, a modulationsystem and a coding rate which are identical to those used when the userdata was transmitted in the previous step, respectively.

(2) The value of data SNR buffer 114 Qprv is updated by being replacedwith past received signal quality Qprv+current received signal qualityvalue Qnow.

(3) Transmission is made through the downlink control channel so as toinform that the transmission data is a retransmission data, themodulation system and the coding system are the same as those employedwhen the user data was transmitted in the previous step. In this case,the terminal is allowed to synthesize the data stored in the receivedsignal buffer 46 with the transmitted data.

(4) The user data is again transmitted.

FIG. 9 illustrates a relationship between the data retransmissioncarried out in the base station of FIG. 8 and the received signalquality at the terminal.

In FIG. 9, reference {circle over (1)} represents a step of transmittingnew data by using a certain transmission parameter. A reference a istaken as the received signal quality Qnow at this time. In the exampleshown in FIG. 9, it is determined in the terminal that the datatransmitted in the first transmission contains some error. Therefore, itis assumed that the terminal transmits a NACK signal to the basestation. In this case, the NACK signal means a retransmission requestmessage requesting that a transmission shall be retried.

The case of step {circle over (2)} holds an expression of inequality,a(Qpvr)<b(Qnow)+THx. Thus, the aforementioned retransmission processingof No. 5 is carried out. The retransmission data is again transmitted byusing a parameter identical to that of the step of {circle over (1)}.The updated receive signal quality at the step of {circle over (2)} isQprv+Qnow, and hence it becomes a+b.

In the case of FIG. 9, some error is detected in the retransmission dataof {circle over (2)} on the side of terminal. Therefore, the terminaltransmits a NACK signal to the base station, and the identical data isagain transmitted at the step of {circle over (3)}. Also the step{circle over (3)} holds an expression of inequality,a+b(Qpvr)<c(Qnow)+THx. Thus, the aforementioned retransmissionprocessing of No. 5 is carried out. The retransmission data is againtransmitted by using a parameter identical to that of the step of{circle over (1)}. The updated receive signal quality at the step of{circle over (3)} is Qprv+Qnow, and hence it becomes a+b+c.

Also, in the case of FIG. 9, some error is detected in theretransmission data of {circle over (3)} on the side of terminal.Therefore, the terminal transmits a NACK signal to the base station.However, the case of {circle over (4)} holds an expression ofinequality, a+b+c(Qpvr)>d(Qnow)+THx. Thus, the aforementionedretransmission processing of No. 3 and 4 are carried out. Whichprocessing is carried out is determined depending on whether there ispower allowable to allocate at the timing point of, i.e., whether thesituation holds an expression of inequality, power allowable to beallocated (Pavl)>a+b+c(Qpvr)−d(Qnow)−THx or not.

If sufficient power allowance is prepared, a kind of transmissionparameter, i.e., the transmission power is increased and the datatransmission is retried at the same transmission mode (i.e., the codingrate and the modulation system) as that of the previous step. At thistime, the received signal quality is updated in such a manner thatQprv+Qnow+Pup=a+B+c+d+Pup. If Pup=y, then y=a+b+c−d−THx. Therefore,theupdated received signal quality becomes 2(a+b+c)−THx.

If there is no sufficient power prepared, of the transmission parameter,the transmission mode (coding rate and the modulation system) isdetermined based on the current received signal quality d. Then, thereceived signal quality Qprv stored in the data SNR buffer 114 isupdated by being replaced with the current received signal quality d,and the retransmission data is transmitted to the terminal as new data.

As described above, since the transmission parameter upon retrying thetransmission is altered under consideration of the synthesized gain uponretrying the transmission, an effective retransmission system can beprovided and the redio communication resources can be effectivelyutilized. Further, since the received signal quality message for use inthe adaptive modulation and coding system is utilized to compare thereceived signal quality at the current timing point with the receivedsignal quality at the past transmission, it becomes possible to estimateaccurately the synthesizing gain of the retransmission data.

Now the processing of the base station of FIG. 8 will be furtherdescribed with reference to FIG. 10.

Initially, at step S11, the base station receives a signal transmittedfrom the terminal through the uplink control channel.

That is, the signal transmitted from the terminal through the uplinkcontrol channel is received at the antenna 14 and supplied through thetransmission/reception compatible unit 1 and the inverse spreading unit2 to the power control bit extracting unit 3.

The processing proceeds to step S12 in which the power control bitextracting unit 3 extracts the power control bit from the signal of theuplink control channel supplied thereto and supplies the power controlbit to the power adjusting unit 10. Also, the power control bitextracting unit 3 supplies the signal of the uplink control channel tothe retransmission request message extracting unit 4. Thus, theprocessing proceeds to step S14.

At step S14, the retransmission request message extracting unit 4extracts the retransmission request message from the signal of theuplink control channel supplied thereto, and supplies the retransmissionrequest message to the mode determining unit 111 and the control unit112. Also, the retransmission request message extracting unit 4 suppliesthe signal of the uplink control channel to the received signal qualitymessage extracting unit 5. Further, in step S14, the mode determiningunit 111 and the control unit 112 examine whether the retransmissionrequest message supplied from the retransmission request messageextracting unit 4 is the one requesting the retransmission or not.

At step S14, if it is determined that the retransmission request messageis one requesting the retransmission, then the processing proceeds tostep S20 in which retransmission processing, which will be describedlater on, is carried out and the processing returns to step S11.

Conversely, at step S14, if it is determined that the retransmissionrequest message is one not requesting the retransmission, then theprocessing proceeds to step S15 in which the received signal qualitymessage extracting unit 5 extracts the received signal quality messagefrom the signal of the uplink control channel supplied from theretransmission request message extracting unit 4. Then, theretransmission request message is supplied to the mode determining unit111 and the processing proceeds to step S16.

At step S16, the mode determining unit 111 determines the coding rateand the modulation system (transmission mode) at the adaptive coding andmodulation unit 13 based on the current received signal quality at theterminal which is represented by the received signal quality messagesupplied from the received signal quality message extracting unit 5.

That is, the mode determining unit 111 determines the transmission modeso that, for example, the error rate on the side of the terminal becomesequal to or smaller than a predetermined value based on the currentreceived signal quality at the terminal.

Further, in the step S16, the mode determining unit 111 supplies thedetermined transmission mode information together with the currentreceived signal quality at the terminal to the control unit 112. Then,the processing proceeds to step S17.

At step S17, the control unit 112 supplies the transmission modeinformation supplied from the mode determining unit 111 to the controldata generating unit 8, and the control data generating unit 8 makes thetransmission mode information be included in the transmission parameterindicative of various parameters of the base station upon transmission.Thus, the control data generating unit 8 generates control datacontaining the transmission parameter. The control data is supplied fromthe control data generating unit 8 through the coding and modulationunit 9, the power adjusting unit 10, the spreading unit 11 and thetransmission/reception compatible unit 8 to the antenna 14. Then, thecontrol data is transmitted as a signal of the downlink control channel.

Thereafter, the processing proceeds to step S18 in which the controlunit 112 supplies the transmission mode information supplied from themode determining unit 111 and the information of the current receivedsignal quality at the terminal to the data SNR buffer 114 in which thetransmission mode information and the current received signal qualityinformation are stored in an overwriting manner. Then, the processingproceeds to step S19.

At step S19, new user data for the terminal is transmitted at thetransmission mode determined by the mode determining unit 111.

That is, at step S19, the new user data for the terminal is disposed ina packet and supplied to the adaptive coding and modulation unit 13 as apacket data. The new user data is also supplied to the retransmissiondata buffer 12 and stored therein so that the new user data can respondto the retransmission request.

The control unit 112 controls the adaptive coding and modulation unit 13so that the new user data for the terminal is subjected to the codingprocess and modulation process of the transmission mode which isdetermined by the mode determining unit 111. The adaptive coding andmodulation unit 13 encodes and modulates the user data for the terminalsupplied thereto in accordance with the control of the control unit 112,and supplies the resultant data to the power setting unit 113. The powersetting unit 113 adjusts the transmission power for transmuting a signaloutputted from the adaptive coding and modulation unit 13 so that thetransmission power comes to have a value identical to that utilized upontransmitting the user data in the previous time, and then supplies theresultant value to the spreading unit 11. The spreading unit 11 and thetransmission/reception compatible unit 1 carry out the processingsimilar to those described with reference to FIG. 2 in the followingsteps. As a consequence, the user data is transmitted as a signal of thedownlink data channel from the antenna 14 to the terminal.

As described above, the user data is transmitted. After transmitting theuser data, the processing returns to step S11 and the similar processingis repeated in the following steps.

Next, the retransmission processing at step S20 in FIG. 10 will bedescribed with reference to a flowchart of FIG. 11.

In this retransmission processing, initially, at step S31, similarly tostep S15 of FIG. 10, the received signal quality message extracting unit5 extracts the received signal quality message from the signal of theuplink control channel supplied from the retransmission request messageextracting unit 4, and supplies the message to the mode determining unit111. Further, in step S31, the mode determining unit 111 recognizes thecurrent received signal quality at the terminal represented by thereceived signal quality message supplied from the received signalquality message extracting unit 5 as the received signal quality Qnow ofthis time representing the received signal quality at the terminal upontransmitting the data in this time. Then, the processing proceeds tostep S32.

At step S32, the mode determining unit 111 reads the received signalquality information stored in the data SNR buffer 114 as the receivedsignal quality Qprv in the previous time representing the receivedsignal quality at the terminal upon the previous data transmission.

According to the processing illustrated in the flowchart of FIG. 10,each time the received signal quality message extracting unit 5 extractsthe received signal quality message at step S15, the received signalquality represented by the received signal quality message is stored inthe data SNR buffer 114 in an overwriting manner at step S18.Accordingly, when the processing of step S11 to step S19 of FIG. 10 isrepeated, the received signal quality message extracting unit 5 extractsthe last received signal quality message, and the data SNR buffer 114retains therein the received signal quality information (the previousreceived signal quality information) represented by the received signalquality message extracted in the previous time until the received signalquality information represented by the last received signal qualitymessage is overwritten.

After executing step S32, the processing proceeds to step S33 in whichthe mode determining unit 111 examines whether or not the currentreceived signal quality Qnow is deteriorated as compared with theprevious received signal quality Qprv. That is, the mode determiningunit 111 calculates the received signal difference Qprv−Qnow which meansthe difference between the previous received signal quality Qprv and thecurrent received signal quality Qnow, and examines whether or not thereceived signal difference Qprv−Qnow is larger than a predeterminedthreshold value THx equal to or more than 0 dB, for example.

At step S33, if it is determined that the received signal differenceQprv−Qnow is larger than a predetermined threshold value THx, and hencethe current received signal quality Qnow is deteriorated as comparedwith the previous received signal quality Qprv, the mode determiningunit 111 supplies the result of the determination together with theprevious received signal quality Qprv and the current received signalquality to the control unit 112. Then, the processing proceeds to stepS34.

At step S34, the control unit 112 carries out calculation to obtain themaximum transmission power Pavl of the downlink data channel that is nowallowed to be newly allocated to a single user, and the processingproceeds to step S35. At step S35, the control unit 112 estimates anecessary minimum increased power amount y as a minimum increase amountof transmission power of the downlink data channel which is necessaryfor the terminal to receive the user data with no error, by calculatingan equation of y=Qprv−Qnow−THx, for example.

In this case, the equation for estimating the necessary minimumincreased power amount y is not limited to the above-mentioned one butan equation of y=Qprv−Qnow or the like can be employed.

Thereafter, the processing proceeds to step S36 in which the controlunit 112 examines whether or not the necessary minimum increased poweramount y is equal to or smaller than the maximum transmission power Pavlthat is allowed to be additionally allocated. At step S36, if thenecessary minimum increased power amount y is equal to or smaller thanthe maximum transmission power Pavl that is allowed to be additionallyallocated, then the processing proceeds to step S37 in which the controlunit 112 sets an increased power amount Pup as an increased power amountof the transmission power of the downlink data channel so that theincreased power amount satisfies an expression of y≦Pup≦Pavl. Then, theprocessing proceeds to step S38.

In this case, from the standpoint for seeking effective utilization ofthe resources in the base station, it is desirable for the increasedpower amount Pup to be set to the necessary minimum increased poweramount y. Further, from the standpoint of putting a greater importanceon that the terminal can satisfactorily receive the user data, it isdesirable for the increased power amount Pup to be set to the maximumtransmission power Pavl that is allowed to be additionally allocated (orany value approximate to this value).

At step S38, the control unit 112 controls the power setting unit 113 sothat the transmission power of the downlink data channel as one of thetransmission parameters is increased by increased power amount of Pup.Then, the processing proceeds to step S39.

At step S39, the mode determining unit 111 refers to the data SNR buffer114 to recognize the transmission mode upon transmitting the user datain the previous time (transmission mode upon transmitting the user dataas an object of the retransmission in the previous time) (hereinafterpreferably referred to as previous transmission mode). Then, the modedetermining unit 111 determines so that the transmission mode for thecurrent user data transmission (retransmission) is identical to theprevious transmission mode. Further, at step S39, the mode determiningunit 111 supplies the determined transmission mode information to thecontrol unit 112 and the processing proceeds to step S40.

At step S40, the control unit 112 updates the previous received signalquality Qprv stored in the data NSAR buffer 114 by effecting replacementof Qprv=Qprv+Qnow+Pup. This updated data is supplied to the data SNRbuffer 114 and written therein in an overwriting manner.

In the above-mentioned situation, the user data is again going to betransmitted at the transmission power of the downlink data channel whichis increased by the increased power amount of Pup with respect to thecurrent transmission power. At this time, as described with reference toFIG. 6, the terminal synthesizes the user data (encoded data) which isgoing to be retransmitted and the user data transmitted in the previousstep together. Therefore, it is estimated that the energy per bit of thesynthesized user data comes to have a value deriving from the sum of theenergy per bit of the user data received in the previous step and theenergy corresponding to the current received signal quality Qnow and theincreased power amount Pup. Accordingly, it is expected that, with theuser data retransmission, the received signal quality at the terminal isimproved to be a value deriving from the sum of the previous receivedsignal quality Qprv and the current received signal quality Qnow addedwith the increased power amount Pup. As a consequence, at step S40, thecontrol unit 112 updates the previous received signal quality Qprv byeffecting replacement of Qprv=Qprv+Qnow+Pup.

At step S40, the control unit 112 supplies the transmission modeinformation supplied from the mode determining unit 111 to the controldata generating unit 8 together with the retransmission flag. Thecontrol data generating unit 8 makes the transmission mode informationand the retransmission flag be included in the transmission parameterindicative of various parameters of the base station upon transmission.Thus, the control data containing the transmission parameter is created.This control data is supplied from the control data generating unit 8through the coding and modulation unit 9, the power adjusting unit 10,the spreading unit 11 and the transmission/reception compatible unit 1to the antenna 14. Then, the control data is transmitted from theantenna 14 as a signal of the downlink control channel.

The processing proceeds to step S41 in which the user data of theretransmission to the terminal is transmitted at the transmission modewhich is determined by the mode determining unit 111. Then, theprocessing returns.

That is, as described with reference to FIG. 10, the user data for theterminal is supplied to the adaptive coding and modulation unit 13 andalso supplied to the retransmission data buffer 12 and stored therein.In step S41, the control unit 112 controls the retransmission databuffer 12 so that the user data stored (i.e., user data transmittedthrough the downlink data channel in the previous step and placed underthe retransmission step) is supplied to the adaptive coding andmodulation unit 13 as retransmission data to be transmitted again to theterminal. The control unit 112 controls the adaptive coding andmodulation unit 13 so that the retransmission data is encoded andmodulated at the transmission mode determined by the mode determiningunit 111. The adaptive coding and modulation unit 13 subjects theretransmission data supplied thereto to the coding and modulationprocess in accordance with the control of the control unit 112 andsupplies the resultant data to the power setting unit 113. The powersetting unit 113 increases the transmission power of the signaloutputted from the adaptive coding and modulation unit 13 by theincrease amount Pup with respect to the transmission power upontransmitting the user data as a target of retransmission, in a manner ofcontrol effected at step S38. Then, the power setting unit 113 suppliesthe resultant transmission power to the spreading unit 11. The spreadingunit 11 and the transmission/reception compatible unit 1 carry out theprocessing similar to those described with reference to FIG. 2 in thefollowing steps. As a consequence, the retransmission data istransmitted as a signal of the downlink data channel from the antenna 14to the terminal.

Accordingly, if the current received signal quality Qnow is deterioratedas compared with the previous received signal quality Qprv but thenecessary minimum increased power amount y is equal to or smaller thanthe maximum transmission power Pavl that can be additionally allocated,i.e., the base station has sufficient resources to increase thetransmission power of the downlink data channel by the necessary minimumincreased power amount y, then the data retransmission is effected atthe transmission power added with increased power amount Pup which isincreased as compared with the previous user data transmission That is,the data retransmission is effected at the transmission power increasedby an amount corresponding to the deteriorated amount of received signalquality. Then, the retransmission data is transmitted at thetransmission mode identical to that upon the previous data transmissionstep.

In this case, at step S40, the transmission parameter informationtransmitted through the downlink control channel contains theretransmission flag. Thus, in the aforementioned terminal described withreference to FIG. 6, the user data received in the previous step and thedata of the retransmission (i.e., the user data identical to the userdata received in the previous step) are synthesized together to create again of synthesis.

When the user data received in the previous step and the data ofretransmission are synthesized together, then it is estimated that theuser data obtained by the synthesis comes to have an energy per bitvalue which derives from adding the current received signal quality Qnowand the energy corresponding to the increased power amount Pup together.Therefore, even if the propagation path characteristic uponretransmitting the user data is deteriorated as compared with theprevious (or the first) user data transmission, it becomes possible toobtain a gain by synthesizing the user data received in the previousstep and the retransmission data together. In this way, it becomespossible to reduce a retransmission achieving no gain, with the resultthat the transmission efficiency can be improved.

On the other hand, at step S36, if it is determined that the necessaryminimum increased power amount y is not equal to or smaller than themaximum transmission power Pavl that can be additionally allocated, thenthe processing proceeds to step S42 in which the mode determining unit111 determines a transmission mode based on the current received signalquality in a manner similar to that of step S16 shown in FIG. 10. Then,the transmission mode information is supplied together with the currentreceived signal information Qnow to the control unit 112, and theprocessing proceeds to step S43.

At step S43, the control unit 112 supplies the transmission modeinformation supplied from the mode determining unit 111 to the controldata generating unit 8. The control data generating unit 8 makes thetransmission mode information be included in the transmission parameterrepresenting various parameters of the base station upon transmission,and creates the control data containing the transmission parameter. Thiscontrol data is transmitted from the control data generating unit 8through the coding and modulation unit 9, the power adjusting unit 10,the spreading unit 11 and the transmission/reception compatible unit 1to the antenna 14. Then, the control data is transmitted from theantenna 14 as a signal of the downlink control channel to the terminal.

In this case, the transmission parameter transmitted to the terminaldoes not contain the retransmission flag. This is because theretransmission data will be transmitted as new user data at step S45which will be described later on.

Thereafter, processing proceeds to step S44 in which the control unit112 supplies the transmission mode information and the current receivedsignal quality information Qnow supplied from the mode determining unit111 to the data SNR buffer 114. The information supplied thereto aresaved therein in an overwriting manner and the processing proceeds tostep S45.

The current received signal quality Qnow stored in the data SNR buffer14 in step S44 will be read as a previous received signal quality Qprvwhen the process of step S32 is carried out in the next time.

At step S45, the data of retransmission stored in the retransmissiondata buffer 12 is transmitted as new data at the mode which isdetermined by the mode determining unit 111. Then, the processingreturns.

At step S45, the control unit 112 controls the retransmission databuffer 12 so that the data of retransmission stored in theretransmission data buffer 12 is supplied to the adaptive coding andmodulation unit 13. Further, the control unit 112 controls the adaptivecoding and modulation unit 13 so that the retransmission data is encodedand modulated at the transmission mode determined by the modedetermining unit 111. The adaptive coding and modulation unit 13subjects the retransmission data supplied thereto to the coding andmodulation process in accordance with the control of the control unit112 and supplies the resultant data to the power setting unit 113. Thepower setting unit 113 adjusts the transmission power of the signaloutputted from the adaptive coding and modulation unit 13 so that thistransmission power has a value of default or a value identical to thatupon transmitting the user data in the previous time, for example. Then,the power setting unit 113 supplies the resultant value to the spreadingunit 11. The spreading unit 11 and the transmission/reception compatibleunit 1 carry out the processing similar to those described withreference to FIG. 2 in the following steps. As a consequence, theretransmission data is transmitted as a signal of the downlink datachannel from the antenna 14 to the terminal.

Accordingly, if the current received signal quality Qnow is deterioratedas compared with the previous received signal quality Qprv but thenecessary minimum increased power amount y is not equal to or smallerthan the maximum transmission power Pavl that can be additionallyallocated to, that is, the base station does not have sufficientresources for increasing the necessary minimum increased power amount yfor the transmission power of the downlink data channel, then the dataof retransmission will be placed into a default value or a valuetransmitted at the transmission power identical to that upontransmitting the user data in the previous time and at the transmissionmode determined based on the current received signal quality Qnow.Furthermore, in this case, at step S43, the transmission parametertransmitted through the downlink control channel does not contain theretransmission flag. Therefore, the terminal does not synthesize theretransmission data with the user data received in the previous step.Thus, the retransmission data is to be handled as newly transmitted newuser data.

On the other hand, at step S33, if it is determined that the receivedsignal quality difference Qprv−Qnow is not larger than the thresholdvalue THx, that is, it is determined that the current received signalquality Qnow is not so seriously deteriorated or rather improved ascompared with the previous received signal quality Qprv, then the modedetermining unit 111 supplies the result of determination together withthe current received signal quality Qnow and the previous receivedsignal quality Qprv to the control unit 112. Then, the processingproceeds to step S46.

At step S46, the mode determining unit 111 refers to the data SNR buffer114 to recognize the previous transmission mode, and determines thetransmission mode for transmitting (retransmission of) the current userdata as one identical to the previous transmission mode. Furthermore, atstep S46, the mode determining unit 111 supplies the determinedtransmission mode information to the control unit 112 and the processingproceeds to step S47.

At step S47, the control unit 112 updates the previous received signalquality Qprv in such a manner that Qprv=Qprv+Qnow. The updatedinformation is supplied to the data SNR buffer 114 and stored therein inan overwriting manner.

In the above-described situation, the user data is going to be subjectedto the retransmission step with the transmission power for the downlinkdata channel kept as the current transmission power, i.e., the user datais retransmitted at the transmission power identical to that upon theprevious user data transmission. In this case, as described withreference to FIG. 6, the terminal synthesizes the user data of theretried transmission and the user data received in the previous steptogether. Therefore, it is expected that synthesized user data comes tohave energy per bit which derives from adding the energy per bit of theuser data received in the previous step and the energy corresponding tothe current received signal quality Qnow together. Accordingly, it isassumed that, owing to the user data retransmission, the received signalquality at the terminal comes to have an improved value, i.e., theprevious received signal quality Qprv added with the current receivedsignal quality Qnow. For this reason, at step S47, the control unit 112updates the previous received signal quality Qprv in such a manner thatQprv=Qprv+Qnow.

At step S47, the control unit 112 supplies the transmission modeinformation supplied from the mode determining unit 111 to the controldata generating unit 8 together with the retransmission flag. Thecontrol data generating unit 8 makes the transmission mode informationand the retransmission flag be included in the transmission parameterindicative of various parameters of the base station upon transmission.Thus, the control data containing the transmission parameter is created.This control data is supplied from the control data generating unit 8through the coding and modulation unit 9, the power adjusting unit 10,the spreading unit 11 and the transmission/reception compatible unit 1to the antenna 14. Then, the control data is transmitted from theantenna 14 as a signal of the downlink control channel.

Subsequently, as described above, the processing proceeds to step S41 inwhich the user data of the retransmission to the terminal is transmittedat the transmission mode which is determined by the mode determiningunit 111. Then, the processing returns.

In step S41, the control unit 112 controls the retransmission databuffer 12 so that the user data stored is supplied to the adaptivecoding and modulation unit 13. Further, the control unit 112 controlsthe adaptive coding and modulation unit 13 so that the retransmissiondata is encoded and modulated at the transmission mode determined by themode determining unit 111. The adaptive coding and modulation unit 13subjects the retransmission data supplied there to to the coding andmodulation process in accordance with the control of the control unit112 and supplies the resultant data to the power setting unit 113. Thepower setting unit 113 adjusts the transmission power of the signaloutputted from the adaptive coding and modulation unit 13 so that thistransmission power has a value identical to that upon transmitting theuser data in the previous time, for example, and then supplies theresultant value to the spreading unit 11. The spreading unit 11 and thetransmission/reception compatible unit 1 carry out the processingsimilar to those described with reference to FIG. 2 in the followingsteps. As a consequence, the retransmission data is transmitted as asignal of the downlink data channel from the antenna 14 to the terminal.

Accordingly, if it is determined that the current received signalquality Qnow is not so seriously deteriorated or rather improved ascompared with the previous received signal quality Qprv, theretransmission data is transmitted at the transmission power identicalto that upon transmitting the user data in the previous time and at thetransmission mode identical to that upon transmitting the user data inthe previous time.

In this case, in step S47, the transmission parameter transmittedthrough the downlink control channel contains the retransmission flag.Thus, as described above, the terminal of FIG. 6 synthesizes the userdata received in the previous step and the retransmission data (userdata identical to one received in the previous step) together. In thisway, it becomes possible to obtain a gain deriving from the synthesis.

In this case, the user data received in the previous step and the userdata of the retransmission are synthesized together. Therefore, it isexpected that the synthesized user data comes to have energy per bitvalue which derives from addition of the energy per bit of the user datareceived in the previous step and the energy corresponding to thecurrent received signal quality Qnow together. Moreover, theabove-discussed case is one in which the current received signal qualityQnow is not so seriously deteriorated or rather improved as comparedwith the previous received signal quality Qprv. Therefore, it becomespossible to obtain a gain by synthesizing the user data received in theprevious step and the retransmission data together. In this way,retransmission obtaining no gain can be suppressed and transmissionefficiency can be improved.

FIG. 12 is a flowchart for illustrating a second embodiment of theretransmission carried out at step S20 shown in FIG. 10.

In the embodiment of FIG. 11, the terminal accumulates the receivedsignal quality information upon respective data transmission operationsof from the first user data transmission (the initial user datatransmission) to the previous user data retransmission, wherebyestimation is made on the received signal quality upon synthesizing thedata of retransmission and the user data received in the previous step.In the embodiment of FIG. 12, the received signal quality upontransmitting the data in the first time is directly utilized as anestimated value of the received signal quality at the terminal.

In the embodiment of FIG. 11, at step S40, the previous received signalquality Qprv is updated by calculating the equation Qprv=Qprv+Qnow+Pup.Alternatively, at step S47, the previous received signal quality isupdated by calculating the equation Qprv=Qprv+Qnow. However, in theembodiment of FIG. 12, the received signal quality utilized fordetermining the transmission mode upon transmitting the user data in thefirst time is directly utilized as the previous received signal qualityQprv.

Accordingly, in the retransmission processing of FIG. 12, at steps S60and S67 corresponding to steps S40 and S47, respectively, the previousreceived signal quality information Qprv stored in the retransmissiondata buffer 12 is not updated and left unchanged. But other processingcarried out in steps S51 to S67 are similar to those in steps S31 to S47of FIG. 11. Therefore, description thereof will not be made.

In the embodiment of FIG. 11, the terminal synthesizes the data ofretransmission and the user data received in the previous step aresynthesized together. Therefore, in steps S40 and S47, under theconsideration of the gain deriving from the synthesis, the receivedsignal quality at the terminal is estimated based on the principle thatthe received signal quality Qprv is added with the current receivedsignal quality Qnow one by one.

However, the received signal quality Qnow represented by the receivedsignal quality message transmitted from the terminal is information ofreceived signal quality at a timing point which precedes from the userdata transmission time by a time period corresponding to several frames.For this reason, the real received signal quality at the timing pointwhen the terminal receives the retransmission data can be deviated fromthe received signal quality Qnow represented by the received signalquality message transmitted from the terminal. If the received signalquality recognized by the terminal can be deviated from the receivedsignal quality represented by the received signal quality message, andnevertheless the real received signal quality is estimated byaccumulating the current received signal quality Qnow on the receivedsignal quality Qprv of the previous step, it is difficult to expect highreliability in the estimated value.

Therefore, if the data transmission is made in such a situation whereonly low reliability estimated value can be obtained for the receivedsignal quality by accumulating the current received signal quality Qnowon the received signal quality Qprv of the previous step, the manner ofdata transmission as in the embodiment of FIG. 12 can be employed. Thatis, the received signal quality upon transmitting the data in the firsttime can be directly utilized as the estimated value of the receivedsignal quality at the terminal.

Also by the process of retransmission of FIG. 12, similar to the case ofFIG. 11, retransmission obtaining no gain can be suppressed andtransmission efficiency can be improved.

In the embodiment of FIG. 11, at step S33, the accumulated value of thereceived signal quality deriving from an accumulation from the firstdata transmission to the previous data retransmission is calculated asthe previous received signal quality in such a manner that the receivedsignal quality difference Qprv−Qnow is obtained by subtracting thecurrent received signal quality Qnow from the previous received signalquality Qprv. However, in an embodiment shown in FIG. 12, at step S53corresponding to step S33 of FIG. 11, the received signal quality uponthe first data transmission is directly regarded as the previousreceived signal quality Qpvr, and then difference between the previousreceived signal quality Qprv and the current received signal qualityQnow is calculated as the received signal quality difference Qprv−Qnow.

Next, FIG. 13 is a flowchart showing a third embodiment of theretransmission carried out at step S20 of FIG. 10.

While in the embodiments of FIGS. 11 and 12 control is made on thetransmission power of the downlink data channel of the transmissionparameter upon retrying transmission based on the received signalquality Qprv−Qnow, in the embodiment of FIG. 13, control is made on thetransmission mode of the transmission parameter upon retryingtransmission based on the received signal quality difference Qprv−Qnow.

In the embodiment of FIG. 13, processing is carried out from step S91 toS93 in a manner similar to those carried out in steps from S31 to S33.

At step S93 corresponding to step S33, if it is determined that thereceived signal quality difference Qprv−Qnow is larger than thethreshold value THx and hence the current received signal quality Qnowis deteriorated relative to the previous received signal quality Qprv,the mode determining unit 111 supplies information indicative of theresult of the determination together with the current received signalquality Qnow to the control unit 112. Then, the processing proceeds tostep S94.

At step S94, the mode determining unit 111 refers to the data SNR buffer114 to recognize the previous transmission mode and examines whether ornot a transmission mode lower than the previous transmission mode by twomodes is prepared in the data SNR buffer 114.

While in the case of aforementioned FIG. 3 description is made on anassumption that merely three transmission modes are prepared forsimplifying the description, in this embodiment a plural number oftransmission modes, or three or more transmission modes are prepared.Further, each of the transmission modes is numbered from a smallernumber to a larger number in such a manner that as the terminal canreceive a signal at a received signal quality of stable variation, theterminal is assigned with a coding system or a modulation system tendingto make smaller user data error rate from the statistical standpoint,i.e., a smaller coding rate or a modulation system having a largerintersymbol distance. In this case, if the value of the transmissionmode is small, the noise characteristics thereof will be improved andthe data transmission efficiency is lowered. Conversely, if the value ofthe transmission mode is large, the data transmission efficiency will beimproved but the noise characteristic is deteriorated.

At step S94, if it is determined that a transmission mode lower than theprevious transmission mode by two modes is not prepared, the processingproceeds to step S99 and the processing described below is carried out.

Also, at step S94, if it is confirmed that a transmission mode lowerthan the previous transmission mode by two modes is prepared, theprocessing proceeds to step S95 in which the mode determining unit 111selects a transmission mode lower than the previous transmission mode bytwo modes for the transmission mode for the current user datatransmission (retransmission). Further, at step S95, the modedetermining unit 111 supplies the selected transmission mode to thecontrol unit 112 and the processing proceeds to step S96.

At step S96, the control unit 112 supplies the transmission informationsupplied from the mode determining unit 111 to the control datagenerating unit 8 together with the retransmission flag. The controldata generating unit 8 makes the transmission mode information and theretransmission flag to be included in the transmission parameterindicating the various parameters of the base station upon transmissionso that control data containing the transmission parameter is created.The control data is supplied from the control data generating unit 8through the coding and modulation unit 9, the power adjusting unit 10,the spreading unit 11 and the transmission/reception compatible unit 1to the antenna 14, and transmitted from the antenna 14 as a downlinkcontrol channel.

Thereafter, the processing proceeds to step S97 in which the controlunit 112 supplies the transmission information supplied from the modedetermining unit 111 and the current received signal quality Qnow at theterminal to the data SNR buffer 114 so as to store therein in a mannerof overwriting. Then, the processing proceeds to step S98.

At step S98, the user data to be retransmitted to the terminal istransmitted at the transmission mode selected by the mode determiningunit 111. Then, the processing returns.

In step S98, the control unit 112 controls the retransmission databuffer 12 so that the user data stored in the buffer is supplied to theadaptive coding and modulation unit 13. Further, the control unit 112controls the adaptive coding and modulation unit 13 so that theretransmission data is encoded and modulated at the transmission modedetermined by the mode determining unit 111. The adaptive coding andmodulation unit 13 subjects the retransmission data supplied thereto tothe coding and modulation process in accordance with the control of thecontrol unit 112 and supplies the resultant data to the power settingunit 113. The power setting unit 113 adjusts the transmission power ofthe signal outputted from the adaptive coding and modulation unit 13 sothat this transmission power takes a default status or has a valueidentical to that upon transmitting the user data in the previous time,for example, and then supplies the resultant value to the spreading unit11. The spreading unit 11 and the transmission/reception compatible unit1 carry out the processing similar to those described with reference toFIG. 2 in the following steps. As a consequence, the retransmission datais transmitted as a signal of the downlink data channel from the antenna14 to the terminal.

Accordingly, if the current received signal quality Qnow is deterioratedas compared with the previous received signal quality Qprv, the basestation transmits the retransmission data at a transmission mode whichgreatly lowers the error rate at the terminal (in this case, atransmission mode lower than the previous transmission mode by twomode).

In this case, at step S96, since the transmission parameter transmittedthrough the downlink control channel contains the retransmission flag,as described above, the terminal of FIG. 6 synthesizes the user datareceived in the previous step and the retransmission data (user dataidentical to the user data received in the previous step) together.Thus, it becomes possible to obtain a synthesized gain, with the resultthat retransmission operation creating no gain can be suppressed andtransmission efficiency can be improved.

In this case, the transmission mode upon transmitting the user data inthe previous step can be different from the transmission mode upontransmitting (retransmitting) the current user data. However, as forexample described with reference to FIG. 6, even if the user datatransmitted in the previous step is different from the current user data(retransmission data) in the transmission mode, it is possible for theuser data demodulating and decoding unit 39 to synthesize these datatogether by synthesizing them in the state of coded data.

In the terminal of FIG. 6, the synthesizing of the user data can becarried out on either of the data which are demodulated by the user datademodulating and decoding unit 39 or the user data which are demodulatedand further decoded by the same unit. In these cases, however, thepieces of user data to be synthesized together shall have the sametransmission mode. In the embodiment of FIG. 11 (and also the embodimentof FIG. 12), it is to be noted that the pieces of user data have thesame transmission mode upon sending the retransmission data at step S41.Therefore, in the terminal of FIG. 6, the pieces of user data can becarried out on the state of user data which are simply demodulated bythe user data demodulating and decoding unit 39 or on the state of theuser data which are further decoded by the same unit.

Furthermore, at step S93, if it is determined that the received signalquality Qprv−Qnow is not larger than the threshold value THx, that is,the current received signal quality Qnow is not so seriouslydeteriorated or rather improved as compared with the previous receivedsignal quality Qprv, the mode determining unit 111 supplies the resultof determination to the control unit 112 together with the currentreceived signal quality Qnow. Then, the processing proceeds to step S99.

At step S99, the mode determining unit 111 refers to the data SNR buffer114 to recognize the previous transmission mode, whereby examination ismade on whether there is any transmission mode lower than the previoustransmission mode by one mode.

At step S99, if it is determined that there is a transmission mode lowerthan the previous transmission mode by one mode, the processing proceedsto step S100 in which the mode determining unit 111 determines thetransmission mode upon the current user data transmission(retransmission) to be the transmission mode lower than the previoustransmission mode by one mode. Further, at step S100, the modedetermining unit 111 supplies information of the determined transmissionmode to the control unit 112. Thus, the processing proceeds to step S96and subsequently processing similar to those described above are carriedout in steps S96 to S98. Then, the processing returns.

Accordingly, if the current received signal quality Qnow is not soseriously deteriorated or rather improved as compared with the previousreceived signal quality Qprv, the base station transmits theretransmission data at a transmission mode which somewhat lowers theerror rate at the terminal (if the received signal quality is constant)(in this case, a transmission mode lower than the previous transmissionmode by one modes).

Also in this case, as described above, the terminal of FIG. 6synthesizes the user data received in the previous step and theretransmission data (user data identical to the user data received inthe past step) together. Thus, it becomes possible to obtain asynthesized gain, with the result that retransmission operation creatingno gain can be suppressed and transmission efficiency can be improved.

At step S99, if it is determined that there is no transmission modelower than the previous transmission mode by one mode, that is, theprevious transmission mode is the lowest transmission mode, theprocessing proceeds to step S101 in which the mode determining unit 111determines the transmission mode upon the current user data transmission(retransmission) to be the transmission mode identical to the previoustransmission mode. Further, at step S101, the mode determining unit 111supplies information of the determined transmission mode to the controlunit 112. Thus, the processing proceeds to step S96 and subsequentlyprocessing similar to those described above are carried out in steps S96to S98. Then, the processing returns.

Accordingly, if the retransmission is requested but the transmissioncannot be lowered relative to the previous transmission mode, then theretransmission data can be transmitted at the transmission modeidentical to the previous transmission mode.

While in the embodiment of FIG. 13 the transmission mode for theretransmission is lowered relative to the previous transmission mode byone or two modes in accordance with the relationship in terms ofquantity between the received signal quality difference Qprv−Qnow andthe threshold value THx, the transmission mode for the retransmissionmay be lowered or raised relative to the previous transmission mode byother numbers, i.e., an arbitrary number of modes.

Further, in the embodiment of FIG. 13 the transmission mode for theretransmission is lowered relative to the previous transmission mode byone or two modes in accordance with the relationship in terms ofquantity between the received signal quality difference Qprv−Qnow andone threshold value THx. However, the received signal quality differenceQprv−Qnow may be compared with other plurality of threshold values so asto determine what kinds of ranges the value of the received signalquality difference Qprv−Qnow falls in, and the transmission mode forretransmission may be controlled depending on the determined range.

Furthermore, in the embodiment of FIG. 13, at step S97, the receivedsignal quality Qnow is stored in the data SNR buffer 114 in a manner ofoverwriting so as to update the previous received signal quality Qprvstored in the data SNR buffer 114, by changing it into the currentreceived signal quality Qnow (Qprv=Qnow). However, as described above,if the base station transmits the data retransmission at the changedtransmission mode and the terminal synthesizes the pieces of user data(retransmission data) transmitted at different transmission modestogether, the previous received signal quality Qprv stored in the dataSNR buffer 114 may be updated in accordance with an equation,Qprv=Qprv+Qnow×(data_new/data_original), for example. In this equation,the data_new represents a data quantity of the retransmission data (dataquantity of the original data except for the error correcting code) andthe data_original represents a data quantity of the user datatransmitted in the previous step.

FIG. 14 is a flowchart showing a fourth embodiment of the retransmissionprocessing at step S20 of FIG. 10.

In the embodiments of FIGS. 11 and 12 the transmission power uponretransmitting data is controlled based on the received signal qualityQprv−Qnow, and in the embodiment of FIG. 13 the transmission mode uponretransmitting data is controlled based on the received signal qualityQprv−Qnow. However, in the embodiment of FIG. 14 both of thetransmission power upon retransmitting data and the transmission modeupon retransmitting data can be controlled based on the received signalquality Qprv−Qnow.

Now the retransmission processing of FIGS. 11 and 12 is referred to asretransmission at a changed transmission power and the retransmissionprocessing of FIG. 13 is referred to as retransmission at a changedtransmission mode. In the embodiment of FIG. 14, initially, at stepS111, the control unit 112 examines whether the base station can affordto allocate additional resources or not.

At step S111, if it is determined that the base station can afford toallocate additional resources, the processing proceeds to step S112 inwhich the retransmission processing at the changed transmission powerdescribed with reference to FIGS. 11 and 12 is carried out. Then, theprocessing returns.

Also, at step S111, if it is determined that the base station cannotafford to allocate additional resources, the processing proceeds to stepS112 in which the retransmission processing at the changed transmissionmode described with reference to FIG. 13 is carried out. Then, theprocessing returns.

Therefore, according to the embodiment of FIG. 14, if the base stationcan afford to allocate additional resources, the retransmissionprocessing at the changed transmission power is carried out while if thebase station cannot afford to allocate additional resources, theretransmission processing at the changed transmission mode is carriedout.

While in the embodiment of FIG. 14 the retransmission processing at thechanged transmission power or the retransmission processing at thechanged transmission mode is carried out depending on the status ofresources in the base station, other scheme can be employed. Forexample, the retransmission processing at the changed transmission poweror the retransmission processing at the changed transmission mode iscarried out depending on the number of terminals communicating with thebase station.

Further, when the retransmission processing is carried out, a target ofchange (control) may not be limited to only either of the transmissionpower or the transmission mode. That is, both of the transmission powerand the transmission mode may be changed simultaneously.

Further, when the retransmission processing at the changed transmissionpower is carried out at step S112, in addition to the retransmissionprocessing shown in FIG. 11 or 12, transmission processing describedwith reference to FIG. 15 may be employed.

FIG. 15 is a flowchart showing a fifth embodiment of the retransmissionprocessing effected at step S20 of FIG. 10.

In the embodiments of FIGS. 11 and 12, if the received signal qualitydifference Qnow−Qprov is not larger than the threshold value THx, thatis, the current received signal quality Qnow is not so seriouslydeteriorated or rather improved as compared with the previous receivedsignal quality Qprv, the retransmission data is transmitted at thetransmission power identical to that upon sending the user data in theprevious step. However, according to the embodiment of FIG. 15, if thecurrent received signal quality Qnow is improved as compared with theprevious received signal quality Qprv, the retransmission data istransmitted at the transmission power smaller than that upon sending theuser data in the previous step.

The retransmission processing of FIG. 15 is carried as follows. That is,from step S121 to S135, processing is carried out in a manner similar tothose carried out in steps of from S31 to S45 in FIG. 11.

At step S123 corresponding to step S33, if it is confirmed that thereceived signal quality difference Qprv−Qnow is not larger than thethreshold value THx, that is, the current received signal quality Qnowis not so seriously deteriorated or rather improved as compared with theprevious received signal quality Qprv, the mode determining unit 111supplies the result of determination together with the current receivedsignal quality Qnow and the previous received signal quality Qprv to thecontrol unit 112. Then, the processing proceeds to step S136.

At step S136, similarly to the case of step S46 in FIG. 11, the modedetermining unit 111 refers to the data SNR buffer 114 to recognize theprevious transmission mode, and determines the transmission mode fortransmitting (retransmitting) the current user data as one identical tothe previous transmission mode. Furthermore, at step S136, the modedetermining unit 111 supplies the determined transmission modeinformation to the control unit 112 and the processing proceeds to stepS137.

At step S137, the control unit 112 examines whether the current receivedsignal quality Qnow is larger than the previous received signal qualityQprv, that is, whether the received signal quality is improved or not.

At step S137, if it is confirmed that the current received signalquality Qnow is not larger than the previous received signal qualityQprv, that is, the received signal quality is not improved but not soseriously deteriorated, the processing proceeds to steps S138 and S131sequentially. Thus, the retransmission data is transmitted at thetransmission power identical to that upon sending the user data in theprevious time.

At step A138, similarly to the case of step S47 in FIG. 11, the controlunit 112 updates the previous received signal quality Qprv in such amanner that Qprv=Qprv+Qnow, and supplies the updated information to thedata SNR buffer 114 in which the information is stored therein in anoverwriting manner.

At step S138, the control unit 112 supplies the transmission modeinformation supplied from the mode determining unit 111 to the controldata generating unit 8 together with the retransmission flag. Thecontrol data generating unit 8 makes the transmission mode informationand the retransmission flag be included in the transmission parameterindicative of various parameters of the base station upon transmission.Thus, the control data containing the transmission parameter is created.This control data is supplied from the control data generating unit 8through the coding and modulation unit 9, the power adjusting unit 10,the spreading unit 11 and the transmission/reception compatible unit 1to the antenna 14. Then, the control data is transmitted from theantenna 14 as a signal of the downlink control channel.

Subsequently, the processing proceeds from step S138 to step S131 inwhich, as in the manner of step S41 of FIG. 11, the user data to beretransmitted to the terminal is transmitted at the transmission modewhich is determined by the mode determining unit 111. Then, theprocessing returns.

In step S131, the control unit 112 controls the retransmission databuffer 12 so that the user data stored in the buffer is supplied to theadaptive coding and modulation unit 13. Further, the control unit 112controls the adaptive coding and modulation unit 13 so that theretransmission data is encoded and modulated at the transmission modedetermined by the mode determining unit 111. The adaptive coding andmodulation unit 13 subjects the retransmission data supplied thereto tothe coding and modulation process in accordance with the control of thecontrol unit 112 and supplies the resultant data to the power settingunit 113. The power setting unit 113 adjusts the transmission power ofthe signal outputted from the adaptive coding and modulation unit 13 sothat this transmission power has a value identical to that upontransmitting the user data in the previous time, for example, and thensupplies the resultant value to the spreading unit 11. The spreadingunit 11 and the transmission/reception compatible unit 1 carry out theprocessing similar to those described with reference to FIG. 2 in thefollowing steps. As a consequence, the retransmission data istransmitted as a signal of the downlink data channel from the antenna 14to the terminal.

Accordingly, if it is determined that the current received signalquality Qnow is not so seriously deteriorated but improvement is notconfirmed as compared with the previous received signal quality Qprv,the retransmission data is transmitted at the transmission poweridentical to that upon transmitting the user data in the previoustime-and at the transmission mode identical to that upon transmittingthe user data in the previous time.

In this case, in step S138, the transmission parameter transmittedthrough the downlink control channel contains the retransmission flag.Thus, as described above, the terminal of FIG. 6 synthesizes the userdata received in the previous step and the retransmission data (userdata identical to one received in the previous step) together. In thisway, it becomes possible to obtain a synthesized gain.

In this case, the user data received in the previous step and the userdata of the retransmission are synthesized together. Therefore, it isexpected that the synthesized user data comes to have energy per bitvalue which derives from addition of the energy per bit of the user datareceived in the previous step and the energy corresponding to thecurrent received signal quality Qnow together. Moreover, theabove-discussed case is one in which the current received signal qualityQnow is not so seriously deteriorated but improvement is not confirmedas compared with the previous received signal quality Qprv. In otherwords, the current received signal quality Qnow is not very muchdifferent from the previous received signal quality Qprv. Therefore, itbecomes possible to obtain a gain by synthesizing the user data receivedin the previous step and the retransmission data together. In this way,retransmission obtaining no gain can be suppressed and transmissionefficiency can be improved.

On the other hand, at step S137, if it is determined that the currentreceived signal quality Qnow is larger than the previous received signalquality Qprv, that is, the received signal quality is improved, theprocessing proceeds to step S139 in which the control unit 112calculates an equation Pdown=Qnow−Qprv, for example, to obtain thedecreased power amount Pdown as a decreased power amount of thetransmission power for the downlink data channel. Further, at step S139,the control unit 112 controls the power setting unit 113 so that thetransmission power for the downlink data channel as one of thetransmission parameters is decreased by the decreased power amountPdown. Then, the processing proceeds to step S140.

At step S140, the control unit 112 updates the previous received signalquality Qprv in such a manner that Qprv=Qprv+Qnow−Pdown. The updatedinformation is supplied to the data SNR buffer 114 and stored therein inan overwriting manner.

In the above-described situation, the user data is going to be subjectedto the retransmission step with the transmission power for the downlinkdata channel changed from the transmission power upon sending the userdata as a target of retransmission in the previous step into onedecreased by the decreased power amount Pdown. In this case, asdescribed with reference to FIG. 6, the terminal synthesizes the userdata of retransmission (or the coded data of the same) and the user datareceived in the previous step together. Therefore, it is expected thatsynthesized user data comes to have energy per bit which derives fromadding the energy per bit of the user data received in the previous stepand the energy corresponding to a subtracted value which is created bysubtracting the increased power amount Pup from the current receivedsignal quality Qnow. Accordingly, it is assumed that, owing to the userdata retransmission, the received signal quality at the terminal comesto have an improved value, i.e., the previous received signal qualityQprv added with the current received signal quality Qnow and furthersubtracted by the decreased power amount Pdown. For this reason, at stepS140, the control unit 112 updates the previous received signal qualityQprv in such a manner that Qprv=Qprv+Qnow−Pdown.

At step S140, the control unit 112 supplies the transmission modeinformation supplied from the mode determining unit 111 to the controldata generating unit 8 together with the retransmission flag. Thecontrol data generating unit 8 makes the transmission mode informationand the retransmission flag be included in the transmission parameterindicative of various parameters of the base station upon transmission.Thus, the control data containing the transmission parameter is created.This control data is supplied from the control data generating unit 8through the coding and modulation unit 9, the power adjusting unit 10,the spreading unit 11 and the transmission/reception compatible unit 1to the antenna 14. Then, the control data is transmitted from theantenna 14 as a signal of the downlink control channel.

Subsequently, the processing proceeds from step S140 to step S131 inwhich, as in the manner of step S41 of FIG. 11, the user data to beretransmitted to the terminal is transmitted at the transmission modewhich is determined by the mode determining unit 111. Then, theprocessing returns.

In step S131, the control unit 112 controls the retransmission databuffer 12 so that the user data stored in the buffer is supplied to theadaptive coding and modulation unit 13. Further, the control unit 112controls the adaptive coding and modulation unit 13 so that theretransmission data is coded and modulated at the transmission modedetermined by the mode determining unit 111. The adaptive coding andmodulation unit 13 subjects the retransmission data supplied thereto tothe coding and modulation process in accordance with the control of thecontrol unit 112 and supplies the resultant data to the power settingunit 113. The power setting unit 113 adjusts the transmission power ofthe signal outputted from the adaptive coding and modulation unit 13 sothat, as is controlled in step S139, the user data as a target ofretransmission is changed from the transmission power upon transmittingthe data in the previous time to one decreased by the decreased poweramount Pdown. Thereafter, the power setting unit supplies the resultantvalue to the spreading unit 11. The spreading unit 11 and thetransmission/reception compatible unit 1 carry out the processingsimilar to those described with reference to FIG. 2 in the followingsteps. As a consequence, the retransmission data is transmitted as asignal of the downlink data channel from the antenna 14 to the terminal.

Therefore, if the current received signal quality Qnow is improved ascompared with the previous received signal quality Qprv, theretransmission data is transmitted at a transmission power smaller thanthat upon sending the user data in the previous step by an amountcorresponding to the improvement.

In this case, in step S140, the transmission parameter transmittedthrough the downlink control channel contains the retransmission flag.Thus, as described above, the terminal of FIG. 6 synthesizes the userdata received in the previous step and the retransmission data (userdata identical to one received in the previous step) together. In thisway, it becomes possible to obtain a synthesized gain.

Further, in this case, since the transmission power for theretransmission is decreased, it becomes possible to avoid an event inwhich the retransmission is carried out at a transmission powerexceeding a transmission power which is necessary for the terminal toreceive the user data satisfactorily. Accordingly, the transmissionpower can be prevented from being consumed uselessly, the energy savedby preventing the useless consumption can be allocated to transmissionpower for another terminal, and hence the transmission power can beeffectively controlled.

In more detail, when the current received signal quality Qnow isimproved as compared with the previous received signal quality Qprv, ifthe transmission power is made smaller than that upon sending the userdata in the previous step by the decreased power amount Pdown(=Qnow−Qprv), the terminal can obtain sufficient gain by an amountcorresponding to the improved level of the received signal quality at ahigh possibility. Therefore, if the current received signal quality Qnowis improved as compared with the previous received signal quality Qprv,it is reasonable for the transmission power for the data retransmissionto be made small as compared with that upon sending the user data in theprevious step. With this arrangement, it becomes possible to obtainsufficient synthesizing gain and energy can be effectively utilized forthe transmission power.

Now description will be made on that the processing of theabove-described mode determining unit 111 and the control unit 112 canbe effected on the hardware base or software base. If a series ofprocessing is carried out based on a software, a program constitutingthe software is installed in a general-purpose computer or the like.

FIG. 16 is a diagram showing an arrangement of one embodiment as acomputer having a program for executing the above-described series ofprocessing.

The program may be recorded in advance in a hard disc 205 or a ROM 203as a recording medium provided within the computer.

Alternatively, the program may be stored (recorded) temporarily orpermanently in a removable recording medium 211 such as a flexible disc,a CD-ROM (Compact Disc Read Only Memory), MO (Magneto Optical) disc, aDVD (Digital Versatile Disc), a magnetic disc, or a semiconductormemory. These kinds of removable recording medium 211 may be offered asa package software.

The program may be installed from the above-described removablerecording medium 211 into the computer, or alternatively, the programmay be transferred from a download site through an earth satellite suchas a digital broadcast satellite to the computer in a radio transmissionmanner. Furthermore, the program may be transferred from the downloadsite through any network such as a LAN (Local Area Network), theinternet to the computer in a cable communication manner. The computermay receive the program transferred in the above manner at acommunicating unit 208 and the program may be installed in the hard disc205 provided in the computer.

The computer has a CPU (Central Processing Unit) 202 provided therein.The CPU 202 is connected with an input/output interface 210 through abus 201. When a user operates an input unit 207 composed of a keyboard,a mouse, a microphone or the like to enter a command and the command issupplied to the CPU 202 through the input/output interface 210, theprogram stored in the ROM (Read Only Memory) is executed in accordancewith the command. Alternatively, the CPU 202 loads the program on theRAM (Random Access Memory) 204 and executes the program. The program maybe obtained by reading the hard disc 205 having the program storedtherein, by being transferred through the satellite or the network andreceived at the communicating unit 208 and installed in the hard disc205, or by reading from the removable recording medium 211 attached tothe drive 209. In this way, the CPU 202 carries out the processing inaccordance with the above-described flowchart. Alternatively, thearrangement shown in the above block diagram carries out the processing.Thereafter, the CPU 202 generates the result of processing through theinput/output interface 210, for example, to an output unit 206 composedof a LCD (Liquid Crystal Display) depending on necessity. Alternatively,the result of processing may be transmitted from the communicating unit208, recorded in the hard disc 205, or subjected to any otherprocessing.

In this specification, the processing steps describing the program formaking the computer carry out the various processing should not bealways processed in the chronological sequence which is illustrated inthe flowchart. The description of the present specification intends toinclude a manner of processing in which these processing steps areexecuted in a parallel fashion or executed separately (e.g., parallelprocessing or object oriented processing).

Further, the program may be processed by a single unit of computer or bya plural units of computers in a distributed manner. Further, theprogram may be transferred to a computer far away from the communicationsystem and executed in the computer.

The present invention can be applied to any kinds of communicationsystems in which the base station can acquire information of thereceived signal quality at the terminal and which employs the Hybrid-ARQsystem.

For example, if the communication system employs a W-CDMA system, theterminal transmits a received signal quality message indicating thereceived signal quality at the terminal, to the base station. Therefore,the base station can acquire the received signal quality informationfrom the received signal quality message.

On the other hand, if the communication system employs an HDR (High DataRate) system, for example, the terminal determines the transmission modeto be requested from the base station based on the received signalquality thereat, and the base station can receive the transmission mode.Also in this case, the base station can estimate the received signalquality at the terminal based on the transmission mode transmitted fromthe terminal.

Accordingly, the present invention can be applied to not only acommunication system such as the W-CDMA system in which the terminaltransmits the received signal quality message, but also a communicationsystem in which the terminal transmits the transmission mode.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, it becomespossible to suppress retransmission operation obtaining no gain andimprove the transmission efficiency.

1. In a transmission apparatus capable of retransmitting data to aterminal for receiving data based on a Hybrid-ARQ (Automatic repeatReQuest) system, said transmission apparatus is characterized bycomprising: differential information calculating means for carrying outcalculation to obtain differential information regarding the differencein received signal qualities at said terminal; control means forcontrolling a transmission parameter upon transmitting said data to saidterminal based on said differential information; and transmitting meansfor transmitting said data to said terminal in accordance with saidtransmission parameter.
 2. The transmission apparatus according to claim1, characterized in that said transmission parameter is a transmissionpower upon transmitting said data.
 3. The transmission apparatusaccording to claim 1, characterized by further comprising: coding andmodulation means for coding and modulating said data, wherein saidtransmission parameter is one of a coding system for coding said dataand a modulating system for modulating said data.
 4. The transmissionapparatus according to claim 1, characterized in that said differentialinformation is one indicative of difference between quality of areceived signal at the current stage and quality of a received signalupon first data transmission recognized by said terminal.
 5. Thetransmission apparatus according to claim 1, characterized in that saiddifferential information is one indicative of difference at the terminalbetween a quality value of a received signal at the current step and aquality value derived from accumulation of quality-values of receivedsignals upon respective data transmissions from the first step to theprevious step.
 6. The transmission apparatus according to claim 1,characterized by further comprising: receiving means for receiving areceived signal quality message transmitted from said terminal andindicative of a quality of a signal recognized at said terminal uponreceiving the signal, wherein said differential information calculatingmeans carries out calculation to obtain said differential information byusing said received signal quality message received by said receivingmeans.
 7. In a method for controlling signal transmission for use in atransmission apparatus which is capable of retransmitting data to aterminal for receiving data based on a Hybrid-ARQ (Automatic repeatReQuest) system, said method is characterized by comprising the stepsof: calculating differential information to obtain differentialinformation regarding the difference in the received signal qualities atsaid terminal; and controlling a transmission parameter upontransmitting said data to said terminal based on said differentialinformation.
 8. In a program for making a computer carry out control insignal transmission on a transmission apparatus which is capable ofretransmitting data to a terminal for receiving data based on aHybrid-ARQ (Automatic repeat ReQuest) system, said program ischaracterized by comprising the steps of: calculating differentialinformation to obtain differential information regarding the differencein the received signal qualities at said terminal; and controlling atransmission parameter upon transmitting said data to said terminalbased on said differential information.